Ammunition regeneration is something available to all characters, just for a specific weapon. Roland with combat rifles and shotguns, Lilith with SMGs, Mordecai with sniper rifles and pistols, and Brick, with rocket launchers. Brick's mod doesn't work according to the wiki, and Roland also has Support Gunner COM for all guns and team members.
Update: I guess that with the downloads the Boarderlands team fixed the part where Brick's mod did not work. I have a mod which allows for regen. and it is working with him just fine. However, before the downloads I have trouble.