Here is a link to some of the best castor oil you can get, it's best to run a degummed castor oil in 2 stroke engines, it can actually be ran straight without any other oils in the fuel mix, it will smoke real nice, but it protect and engine like crazy too and of coarse then there is that great castor smell........!
This is a sight I use to get the materials for the fuel I will be mixing myself for mine and a friends RC trucks buggies and planes, a mix of 5% castor with 10% red line synthetic for a 15% oil mix fuel RC fuel is real nice.
Anyway, $20.00 per gallon for this great oil is a steal.
Since you like to run a bit of castor Tom this would fix you right up at a good price.
Fox 100% castor oil - $20.00 : Fox Manufacturing
For anyone interested in the Red Line oils here is a link to there site as well.
Red Line Synthetic Oil - Two-Stroke Oils