My local hardware store carries the sanding drums, but they seemed to last about 5 revolutions. My welding supplier just ordered me in bulk quantity of them (Nortons in 3/4 and 1-1/2 dia) in various grits, they seem to last a bit longer than the blister packs at the hardware store, but still wear out sooner than you'd expect. At least the bulk qty got me a better price...
Not too much shop time this weekend, but I did manage to test fit the tailgate to see how well it matched the new radiuses added to the opening.
There are a couple areas the gaps will need tweaking, but the "new" corners should help add to the other subtle changes.