I found one gasket locally... still looking.
However, I' really having a dickens of a time with these kegs... with a good deal of fiddling around, switching lids and rings and such, I've managed to get a good seal on 2 of 4 kegs. (And we had an after-classes party last night and they worked well!)
The last 2 kegs though, I'm completely beside myself trying to get a seal.. even with the new ring, and switching the lids back and forth, and wiggling, pulling up on the handles, etc, I just can't get a seal. There is no apparent damage on keg, lid, or gasket. Any ideas?