Pitch Bender for Roland Fantom FA-76
It's not exactly what you are looking for, but potentiometers' resistive elements often get a bit oxidised as they get older.

Generally, potentiometers are designed to be self-wiping, meaning that cycling the pot back and forth will often break through the oxide layer and restore some of the functionality.
Alternatively, any electronics contact cleaner may be very effective. Just squirt a bit down the sides into the pitch-bend controller, and work it back and forth repeatedly.

As a last ditch attempt, if the above does not work, the wiper may have relaxed a bit, and therefore may not be making good contact with the resistive element in the pot (see the wikipedia article for info on how the internals fit together). It may be possible to disassemble the pitch-bend assembly and manually bend the wiper to help it make better contact.

I realize it may not be information on how to obtain replacement parts, but many companies are a nightmare to deal with regarding obtaining any information about the internals of their products, let-alone parts. It may be worth the time to try and fix the issue yourself before simply trying to replace the defective assembly en-masse.