Thanks for the browser tips. I'll look into it.
The drums are 1"x1" commonly available spiral band sanding sleeves. I include 120 with my machine, as it's a good middle ground that cuts efficiently without deep grooves that lower grits can cause. It's possible to get the sleeves in 36, 80, 240, and 600 grit in various kinds of abrasives. I usually include aluminum oxide sleeves, but you can also get them in ceramic and zirconia, though not in all the same grit options.