The fabled place on 32nd Av... I have heard of it but I can never remember the name of it so I can never look up their #.
At any rate, I did wind up finding some, at my old trusty source for plumbing bits, Western Pump (287-0256). At least they do carry the RVT100 at $8/tube. So I guess it wasn't quite so wild-goose-chase after all.