Assuming you don't want to make a Colloidal Silver generator yourself (it's pretty easy, if you don't mind using a soldering iron, and you know your way around a Radio Shack... heh...), you can grab a very inexpensive one (complete with bottle for storage, glass to make it in, funnel [for straining], silver wires, batteries, and generator) for about $50.00 plus shipping from Sunstone Herbals:
The kit includes instructions. Basically, you pass an electric current through silver wires in a cup of distilled water. (In the case of the above kit, it uses three 9-volt batteries, included.) The longer you do it, the more silver gets taken off one wire and released into the water (in a little cloud). The other wire will accumulate silver oxide (which is black). After twenty minutes or so, you take the wires out, wipe them off with the included wooly scouring pad, swap the wires around (so that the wires get used evenly), and do it for another twenty minutes or so. Then wipe off the wires again and strain the water (coffee filter in funnel) into the bottle (since some of the silver oxide will have come off into the water).
After awhile, the silver will be completely evenly distributed in the water (say, half a day), and it should be a nice, golden color.
The warmer the water you use to make the silver, the higher the concentration. I usually nuke the water for a minute before putting the wires in.