I went the DIY route. Used a 150# static regulator from Cramer-Decker, maybe it was Chicago Pneumatic, don't remember
doesn't matter, and a 5# tank from General Air per Red_Chili (5# is plenty for 31's). Total cost including the tank was around $80 as I has other stuff laying around, QDs, hose, etc. Found out the hard way that the plain 'ol yellow self coiling air doesn't cut it. I order the urethane stuff for another $50
only to find out that its the exact same stuff my wife uses for medical gas in the operating room. Any way she has 1st dibs on a hose IF and when one brakes (rare event). It's more cost effective for them to replace it than repair it.