Rio Grande sells some very nice copper wire for inlaying. One spool should last a lifetime. It now comes in various sizes. A quick search on their web site will show you the options.
I use electric cable copper annealing it, easy to find in a lot of diameters, i make something wrong?
Sorry but sometime the language give me some doubt, is the soft copper a expecial type of copper or is only copper annealed?
I don't inlay brass. It work hardens too quickly and for me, the cost and ease of inlaying gold wire outweighs the amount of time it takes to inlay brass.
Years ago, I found spools of copper wire in the local hardware store---all different gauges too.
For teaching wire inlaying the dead soft copper wire that Andrew suggested from Rio Grande works great, I have a spool 1.00 and it pulls smoothly through my draw plate. J.J.
Try wire-sculpture.com. They have bronze, copper, and brass all in dead soft in a lot of sizes. You can buy by the foot at reasonable prices and shipping is only $4.95.
Scott