Eugene Toy and Hobby stocks Sig all Castor fuel, and the last time I checked Ted's Interstate Hobby (near Delta Park) had Sig fuel in stock.
I'm set. I can get any mix of VP Powermaster or VP Wildcat from a couple of shops, as long as I buy a case of it. But it's not as easy as just dropping into the local R/C Car store! I can also mix fuel here at the house, with any sort of oil or amount of nitro...until I run out of nitro.
The problem is Big Ron's, in Brusly, LA. I think Gil and Mike can turn Ron onto a good fuel source in Red Stick. There is a need to shun the typical 10% R/C "weedkiller", if his Fox .35 is to last more than a few tanks full. I wish him well with that!