I mostly just use solid copper rivets. You can get a small pack at tractor supply, hobby lobby or maybe Michaels, but they are pricey. You can buy them in bulk at the different leather supply places online or Amazon. I like bukleguy, but Amazon is probably the best place to start. You can get a small variety of rivets and a rivet tool for cheap. Copper is softer and easier to work with than brass.
yup - #9 harness rivet & burr sets. 1/2" will handle most of your needs unless you are using serious heavy weight leather, then 5/8 or 3/4. at $28/ pound, 3/4" will cover all your bases if this is an occasional thing.
I picked up some copper rivets from the local ACE to try. I think this is OK. I know brass is more difficult to work but I think I'm going to try some to see.
Reloaded my Sagewood Spools with fresh bankline, black & red electrical tape and 80lb test (20lb diameter) synthetic braided fishing line