That's where I bought mine. Very heavy duty - although I don't use them much if I can sew it instead.
You'll also need a set - DIY or otherwise. This slips over the shaft of the rivet to punch the burr (the washer bit) down onto the rivet; cut the shaft to length then peen it down. The commercial set has a handy hemispherical dent in the end to forn the shaft - although it helps if you bevel the corners that you'll leave when it is cut to length.
If I've got the wrong end of the stick and you're really trying to rivet solid materials together, then go with Ogri's comments - use a small cross pein hammer to spread the rivet material in all directions, then either shape or file flat the head (the latter assuming you countersunk!).
Tube rivets can be made with a couple of small ball pein hammers if you're careful -
http://www.ganoksin.com/borisat/nenam/other-hinge.htm has some good instructions about 1/3 of the way down.