You have already confirmed that the bearings are shot (common for these pumps). I think you have to scrounge around for a new or rebuilt one, as parts are not available (unless you have the skill to do the rebuild yourself)...
...the only purpose of the air pump is to reduce the hydrocarbon emission produced by a cold engine (that produces a richer fuel mixture upon startup). The catalytic converter has the job of breaking down the harmful emissions...on a cold engine, more of that is sent to the cat, and too rich a mixture over a long period of time will destroy it and the O2 sensor.
Once the cat has warmed up sufficiently to do its job effectively, the air pump is no longer needed...that is why you don't here much from it after the first few minutes of running the engine.
As far as damage, if the air pump needed to function continuously while the engine was running, disconnecting it would cause premature failure of the catalytic converter, (as much or more $$$ to replace). I don't know statistically how long the cat could absorb a too-rich mixture if the potential for damage only occurred for a few minutes every time you started the engine.
If you have emissions inspections in your area, make sure your engine has a chance to warm up sufficiently before you head to the inspection station...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car