The helmet started off as a hockey helmet IIRC, the same ones modified for Tron.
The jumpsuits were custom (or at least customized) and although I can remember it being said on the audio commentary for one of the discs (which one escapes me, I've got three different versions of the movie) that the vests were a found item from a local police supplier from Dallas, where the movie was filmed, I haven't been able to back it up or find the quote on the commentary, so they may have been completely custom.
Check out RoboCopArchive.com, on the boards there's a gal by the name of murphy38 who owns almost every RoboCop item you could think of, from screen-used armor to production notes to lunchboxes; she owns a few jumpsuits, which she's had replicated by a seamstress. She may be able to hook you up with some reference material. She's French, however, so be clear in your communication. She's a great girl, she'll help you any way she can.