Because a rivet gun is an air tool, you will need an air compressor to run the rivet gun adequately. Rivet guns do not require a great deal of compressed air. If you have any other air tools, though, you should plan on investing in a 20-gallon tank. This size of tank should have adequate air to keep up with whatever basic air tools you plan on using, including an ACAT rivet gun.
You will also need to make sure your gun is fitted with the proper rivet set for whatever type of rivet you plan on driving. To drive any size of the flush head, you need a single flush set. If you plan on driving universal head rivets or other kinds of raised head rivets, you'll need several different size rivet sets.
You can purchase rivet sets with either long or short shanks to drive the same size rivet. You can even buy curved rivet sets for tricky locations. With so many options, you may wonder where to start. Buy one long cupped rivet set and one short cupped rivet set for the size of rivet you plan on using.
You will also need a bucking bar. The bucking bar consists of a bar of hardened steel with polished ends. A good bucking bar will be at least as heavy as the rivet gun. So if you have a 3lb rivet gun, you should have a 3lb bucking bar.
Whether you have a 3X or 2X ACAT rivet gun, you can find all your rivet gun accessories and necessities at Yardstore.