Try morgan fuels, they make oils with what you want in it. They come in pure castor, synthetic (blue), castor based (pink). All you need to do then is to mix methanol and the amount of nitromethane you require. Look at your engine user manual for oil content, I normally use 18% oil and 25%nitro for 3D plane and !8% oil and 15%nitro heli. I prefer using the pink stuff.