what guns and what input pressure do they like? They make rigs so that you can run air-tools off of a scuba tank but those take the pressure all the way down to 125psi.
I'm guessing you'd need an unbalanced 1st stage scuba regulator. Or you could go cheaper and get a Scuba fill adapter. The big question here is what could take 3500psi input pressure and bring it down into sub 1000psi range for your guns to work off of? Then use a y splitter to 2 remote lines.
My neanderthal self would grab a HPA tank valve/reg and tap the tank side for 1/8" NPT then screw that into an ASA and 2 remote lines and be done with it. But this grab a HPA tank valve/reg and tap the tank side for 1/8" NPT then screw that into an ASA is a sketchy (safety wise) move that I don't know that I'd trust other peoples safety to.
Why run an 80cf tank why not a 100?