Sig sells AA Castor Oil by the pint, quart, or gallon:

$6.79 per pint
$10.46 per quart
$19.99 per gallon

Sig also sells 20% pure castor fuel in 5%, 10%, and 15% nitro versions; and 25% pure castor fuel in 5% and 10% nitro versions.

It's unfortunate that 25% pure castor oil fuel is ideal for bushed engines like O.S. Max LA series or Thunder Tiger GP series, but it's almost impossible to find at hobby stores any more. I wonder if all of those Avistar Select RTFs at our club would still sound like angry hornets if they were being run with the proper fuel?