Have you tried DickBlick.com
? I used to clip coupons and run around to local hobby shops to buy supplies on sale...and hopefully they were on sale and in stock when I need them. Most often they were not.
Dick Blick has everyday low prices with additional promotions such as free shipping on most orders. You have a larger variety of items that are always in stock AND the best part, I don't have to clip coupons, pray for sales or run around to various stores because they deliver your purchased items right to your front door. I have used DickBlick.com since 2009 and I Love it!
You should try it. You'll probably be as pleasantly surprised as I was to discover them.