Thanks for the link. Those look perfect but are about double what the BMX cogs are selling for on Ebay.

Just thought to consult the Sheldon page on SS and got my answer:

You can use one of the old sprockets from your taken-apart cassette, but it you are less likely to have accidental derailment if you use sprockets made for single-gear us, with longer teeth. BMX cassette sprockets are best. These sprockets are quite inexpensive, and are available in a range of sizes.