What is the reddest red, well you probably should have pyrrole red, ( perhaps pyrrole orange ) , and yes even opera rose and Quin magenta. I like both nickel yellow and benzi yellow. I like the benzi brown too ( daniel smith permament brown, it goes well with benzi yellow ) I like having PB16 ( actual phthalo turquoise ) and diox violet, and all the phthalos.
If you have these are still having an issue, the issue is not the color. You should be able to create convincing color if you just have browns. Color is to put it simply relative, its not an absolute. The problem you are trying to solve is one of absolutes, is this the right color, when the real problem you need to solve is relative color. That is a lesson those starting out in understanding color take a while to figure out.
Luminosity is an illusion, it is really more about mastering how we depict light, in a lot of ways its optical illusion, tricking the viewers mind. To get a bright luminous red, the focus should be less on the red, than on the dark and dull greens. Greens take a great deal of effort to master. The fact is our medium is duller, it will dry back, simply because its not oils. What the color actually is, that is not the problem, its never going to match the actual color.
My suggestion is focus for a while on de-saturated colors - such as the browns, read up on the Zorn palette. ( I am not saying this is how you should paint, I am saying this is something you should do as an exercise until its not impossible for you, after this "clicks" using actually saturated colors suddenly becomes a lot more powerful )
My own ability to get luminous oranges for example, it came when I realized that burnt sienna is an orange, suddenly instead of seeing it like a brown ( it looks completely different than my pyrrole orange ), now I see it as almost the same color as my pyrrole orange. To be honest if they are both in my palette I have trouble seeing which is which, when I started they were obviously different. This happened when I was doing a sunset using just ultramarine, burnt sienna and gold ochre, my version of the zorn palette, and I got the sky to look luminous just via contrast. Suddenly something clicked and how my mind categorized burnt sienna changed, and how I see the world changed.
If you think about it, there is NO WAY to depict colors as luminous as a sunset, when you are on location ANY color is not even close, but when you are no longer there, the question is does it look like a sunset. Is it luminous when its matted and framed. Its not about matching actual colors (absolutes), its about matching the feeling, and using the wrong colors but in the correct relative contrast, the wrong values often is necessary to capture the correct feeling.
This is about learning how to make ANY color work instead of figuring out the perfect color. It is about understanding how to mix color, and why desaturating colors works as a foil. Its like in comedy, people focus on the one delivering the punchline, not noticing the straight man setting up his partner for the perfect joke.
So too is color, think about negative painting, an important skill. Its about defining something not by painting it, but by painting what is not it. Think about how you handle color as much about how you paint what isn't the color, as about painting the specific color.
I have seen some wonderful approaches where the artist simply does a wash across the background using tints of bright colors, pastels even, while its wet into wet. Then they go in with dull and dark colors to not paint the subject, but to paint the background leaving the subject alone, this is done wet on dry, more calligraphy. Again they are doing the bright colors first, very light, but they don't look bright until they go in with the contrasting dark and dull colors.
Now back to green. This is something I learned from Van Goghs Blue irises. There is what I call a base green, a color which is arbitrary really. If you take this color and around it create a circle, you take some red and tint it just enough so its still green but its not brown, to get a red leaning green. Next do the same with yellow, get a yellow leaning green. Blue Leaning. Purple leaning ( this is often actually gray ). Orange leaning. This creates a color wheel of green. The only thing it does not have is a green leaning green. Learn what these greens are, learn to see a green and see where its leaning on the color wheel, as if greens are their own color wheel.
Now what I noticed van gogh did ( after accounting for the fading reds, he used alizarin like colors ), is he put the purple flowers adjacent to the yellowish green, yellow and purple are compliments. The orange earth, he put against the bluish greens. He not only created obvious contrast, but subtle contrast within the greens, knowing that complimentary colors maximize contrast.
He was not using the actual colors he sees, he was adjusting them. Classical artists for example would draw marble statuary, the perfect proportions, then when they would draw a real naked model, if they actually drew her as they saw her, not using marble proportions, they would be sent back to draw marbles. They were made to learn how to interpret what they really saw, thru a lens of ideal and heroic proportions, to exaggerate and convince.
Van Gogh said "Do not quench your inspiration and your imagination; do not become the slave of your model."
Do not be afraid to alter the colors, use more colors than you see, lean the colors, you are not a camera, rather your usage of color is an important part of the composition, it has to make sense independent of the model.
My first suggestion is to just practice practice practice, at some point you will notice the colors just start to pop more, the real issue isn't the paint, its skill level. Buying the brightest paint isn't going to sidestep this learning curve. Instead by my starting with dull colors, its kind of like walking with weights on your ankles and wrists, it makes you work harder, which develops your artistic muscles. Learn how to obtain rich color. This takes a while, but when it pops, you just go ahah, and it becomes intuitive.
My second suggestion is to really study color, take lots of trips to your local art museum, and when you look at pictures, ask why is this so luminous. Take an actual value scale with you. Look for obvious complimentary colors, and subtle ones where its leaning things like the green i described. The thing I notice is pictures often go very very dark, even the bright areas are often as dark as a 30-40% on a value scale.
I also suggest reading this book, Color and Light: A Guide for the Realist Painter (by James Gurney)