You can get it as a dry pigment and mix your own:
https://www.earthpigments.com/green-mc-pigment/#techdata

Pebeo over on Blick seems to carry it in huge tubes, but looks to be a “Studio” quality (for color studies and preparatory paintings before doing a finished work).

That said, I personally just mixing up this hue with PY110 + PB27. It is a beautiful hue, and this handles in very much the same way as the PG8 pigment itself. You can use PB60 to get there as well, but results from that will tint out less vibrantly. Either mix will need to lean more yellow than one might expect initially.

If memory serves (and I may be wrong), Courbet often used the original Hooker’s Green, an admixture of Prussian Blue and Gamboge. For all the concern about lightfastness, his landscapes still look fan-freaking-tastic. Seriously. If you care about art, look for any chance to stand in a room of Courbet landscapes: You’ll feel a gut-punch.

As it happens, Williamsburg makes a green they call Courbet Green. I have some. The online swatch at Blick doesn’t do it justice; it really does resemble the green in Gourbet’s paintings. It’s a concoction of Prussian Blue, Burnt Sienna and Cad Yellow.

Seems to me that an easier way to get there would be to mix Prussian Blue with Indian Yellow, perhaps with some transparent Ochre or Siena. Modern Indian Yellow is pretty close to Gamboge.

Now, if you really want PG8, I wouldn’t dream of trying to talk you out of it. I’m notorious for collecting rare tubes that I will probably never use. Consider Ebay.

It seems odd to me that Hookers Green is not readily available in oils, as it seems to be a standard color for watercolors. I don’t paint much in watercolors, but have done enough to know that many watercolorists rely on it. I’ve never looked for it in oils because I generally mix my own greens. The only tube greens that I use in oils are Sap Green and more recently Perylene Black, which is really just a very dark green. I found out about Perylene Black on these forums and bought a tube because it was inexpensive and I have use for a very dark green in painting landscapes. I am impressed so far and it might end up being the only tube green that I use on my palette.

Russian oil paints [URL=http://www.nevskayapalitra.ru/brands/master_class]Master Class[/URL] contain it, №701 is a mixture of PG 8 and PY1, №716 is PG 8 and PY 83. In its raw form it is available from .

Most extensivelly used green for Russian artists. The lightfastness is equal to naphthol pigments. Actually, PY1 and PY83 has the same lightfastness as PG8 naphthol green. Yellow pigments also gives good light protection for green pigment.