If you need something more than GT100 I don't know where in PA you are but if you are near Phila, I know for sure that K&G Speed Shop on Rt3 just west of I-476 always has C16 and a few other choices too.
From what I've read in the past couple of hours, it looks like the 100 octane unleaded should be fine for a single running 25psi(some have run 28psi). I think Ill give it a try, and hope for the best. It would be nice if there were a cheap way to monitor timing. One plus to this is Im only 10 miles form the station and since its street legal, I can pull in and fill it up without messing with all of the jugs. A local shop has recommended straight C16 for high boost, but im not sure where high boost starts and perhaps C16 is over kill for safety anyway.