Per your request, here's the AVAYA stuff for the 96xx and 46xx phones. Also including the stuff for the other Avaya equipment, as I seem to remember it's referenced in the other two.
The MIB for the 96xx was clean, the one for 46xx needed a small edit. Both now pushed to netdisco-mibs. I didn't included the rest of the MIBs since they are for switch products, but I did notice there was a newer IPX-MIB in that archive so I updated the one in netdisco-mibs.