It might help if you tell us what you need to rivet. In general, Olympic rivets are only used to replace bucked (solid) rivets that are used on the exterior when you don't have access to the inside of the wall to properly buck a rivet. Once shaved, the head of the Olympic rivet will be hard to distinguish from an original bucked rivet. Nearly all the rivets on the interior are conventional "pop" rivets, typically 1/8" in diameter. You can pick these up at your local hardware store, just be sure to get aluminum rivets with an aluminum mandrel. There are pop rivets on the exterior too, holding on bits of trim and the bellypan. These rivets are typically 3/16" in diameter, and especially for the belly pan, you can buy some special pop rivets from VTS that have a very large head.
If you are replacing bucked rivets and can buck in the new rivets, then look at VTS's site. You can buy a complete starter kit for buck riveting, and you will need relacement solid rivets, which VTS also sells in a 5/32" diameter to fill up the hole that will inevitably get enlarged when you drill out the original rivets.