I bought the purple 3M paper at Home Depot. In my store it is in the spraypaint aisle but YMMV.
I bought 60, 80, 100, 120, 180, and 220 grit. Not sure if it goes any finer because it is NOT Wet-or-Dry paper.
Excellent stuff!
Do they come in 20 sheet packs or 5 sheet packs. It's too bad they don't have a variety packs.