Patrick,
I really like the Arkel and Jandd products previously mentioned. If you're looking for
something a little more robust than the small replacement parts, have a look at some of the parts at the
VeloFred web site....here's a link to some of their pannier products:
http://www.velofred.com/index.php?cPath=214_257
Incidentally, I happen to sew my own rando bags and panniers. I have
used the KLICKfix mounts by Rixen & Kaul. I am very pleased with the
quality, however it was a pretty pricey especially when you make your own bags to save money. I am attaching a couple images of a pannier that I made with the R&K attachment rail stuck to the back---it's a pretty versatile piece that mounts and locks into place very quickly.