What, full auto or semi?
Nearest you will reliably get (ie without taking meat off of sears) would be an RT Automag, with about 900psi going into it from an air system.
Gaz
Yup an RT can almost be classed as full auto if you find the sweetspot on the trigger and you get the input pressure right. I think most tournament ban you from doing this.
ATS has full range of autos and the M4 RAM which is made by Asia Paintball Suplly (asiapaintball.com) is a clip fed mechanical auto (it ejects shells and everything!), but it shoots .43 caliber paintballs.
an old tippman marker called an s.m.g. is a full auto non electro. it has the look of a side feed sten gun (verry cool) you can find them at online auctons. it does take an odd caliber paint though.