Piece of cake!
Buy one of those R-134 conversion kits that are sold just about everywhere. They have the tap and adaptor fittings in the kit.
Some places even sell just the adaptor fittings, but those are harder to find, and not much cheaper. So you wind up with 3 extra cans of R-134 and some lube, no big deal.
I hear the Feds crack down pretty hard on these blackmarket vendors if they catch them. They are treated sort of like drug dealers. Doubt they would go after the users, though you never know...
1986 300E 5-Speed 240k mi.