Thanks everyone.
I used to mix my fuel, but gave away all my supplies before moving. I will probably start again, but wanted to buy some before then. Yes, I've been trying to buy it from Brodak, but the sale has not been going through. Brodak has exactly the same mix that I developed on my own, and it works well. 35% nitro sometimes runs a little faster, but the engine run doesn't last as long. 20% oil is usually ok, but 22% seems better when the engine has good compression.
I don't want to just use any old fuel. When teaching kids, I like to have good-performing planes that can do loops and have good power. It's like trying to teach a child to fish while using a fishing rod/reel made for kids. They don't work well and are not the best way to get them interested.