Just about anything "gas tight" has at one time or another been used. Many (most) I personally disagree with, such as the "good ol' boy" using a one pound propane gas bottle to drive an airbrush. Hopefully he hasn't blown himself up, yet. Over the years, Propane and Freon tanks have served many as "git by" tanks. Eliminating ALL the residual gas is important, but the big issue is the relatively light gauge sheet metal that they have been made from. Although rated as a pressure tank, they can (and do) rupture.
I personally would want an "ASME" rated tank. A non-ASME tank should be available at most any car parts store as a tire filling tank. For a true ASME tank, WWGrainger would be a starting point. Mostly because they're close to me, I'm sure there are many sources.
If you're not concerned about the rating, a cheap Wally World compressor might be cheaper. I have several tire tanks as "buffers" on long air lines. Such as for a nailer. . . The long hose with small ID has a lot of losses for high volumn, short duration work like a nailer. A buffer tank close by fills many shortcomings there. Mine is rigged with the same fittings as on the hoses. A piece of cake to add a pressure switch and gauge to the lash-up.
I once stumbled over a DeVilbis pump with an ASME tank at a Sears store. It was labled Craftsman, but priced as a low end pump. I couldn't get the money out fast enough. Many (most?) Craftsman air pumps had non-rated tanks. This one had the giveaway pipe plug in one end. (33 Gal)
I (again, personal opinion) won't waste money on an "oil-less" pump. They are a marketing gimmik for cheap air pumps, nothing more. Mechanically they won't hold up in the long term. Same for the tank on a compressor, ASME or do without. But there are, and have been for years, many "git-bys" for air tanks. It all depends on pressure, volumn, and anti-rupture capabilities. And residual gasses. . .
.