Rivet sets are available at least at these vendors and probably others. You'll probably want the .410 tool size, which is most common, and for RVs, probably ought to get -3 and -4 universal-head rivet sets, as well as flat sets for flush-head rivets. There are other related tools, like bucking bars or back-rivet sets and plates, which a builder will need, plus clecos and various deburring tools. The list gets endless.
VAF has a tool section that contains much excellent information.
I have an ingersoll pneumatic drill and it has a trigger which isn't a feathering trigger. While I don't know what your rivet gun has, if the trigger is abrupt, I'd recommend replacing the gun with either a Sioux rivet gin or a less-expensive Acat brand, which is probably only available from the yardstore.com. I'm building my RV-3B with an Acat gun and like it better than the expensive Sioux gun that broke years ago.