What you start with will depend on the shape of the tool when you start. If it is reasonable shape, square edge, decent bevel without any nicks you could start with something around 220 grit probably.

Then moved to a 320 or 400. Then 600, and 1000 or 1200. I went to 2000 grit. When I got done, the polished edge looked like a mirror and it would shave the hair off you arm no problem.

If I was just resharpening one I would start with the 600 grit. As long as the edge wasn't nicked or damaged. If you don't have one, get you one of those cheap little roller jigs to hold the irons in.

As for a source, most any auto parts that also sells painting supplies (probably not Auto Zone, Carport and the Wal Mart's of Auto Parts) will have a good selection of Wet/Dry paper. The Borg's will have it to 400 grit.

It works amazingly well. But I got tired of it and bought me a Makita Knife Sharpener.