Funny, while I'd never regard Gauss ammo as scarce, I'v never had a serious problem with it. I've managed with Gauss weapons on three party members (Cassidy, Vic, and either the Brain-bot or Lenny) and nobody ever ran out. I was at the time using a combo myself of a Gauss rifle and a situational big gun (i.e. using a rocket or a burst weapon depending on situation). I usually had another weapon as a backup, something like a Grease Gun or a Thompson in case I ran into a bunch of rats or something, but that was my only ammo conservation practice.
Just for openers, you can really stock up on Gauss weapons in sf if you want to.
Female Tanker Punk: Gauss Rifle +100 rounds
Marc (on Tanker): Gauss Rifle + 100 rounds
(both of the above are in their normal inventories so stealing works best)
Two guards in the Steel Palace: 100 rounds apiece
Combined with the Gauss pistol from the Mariposa base, you should have all the Gauss weapons you need. Possibly one more rifle for Vic once he's doing two attacks a round with it.
There's loads of Gauss ammo on the Enclave, but Bozar users should be careful, there's no .223 FMJ.