Jason,
Boca bearings sells them. http://www.bocabearings.com/
I'm not sure if the silicon nitride bearing made much improvement. It certainly did not make the magnitude of difference that changing the oil to Mobil SHC634 did (that's a huge upgrade). I'd recommend trying to get hold of a quart of SHC634 and relube the existing bearing before trying a ceramic ball.
Boca bearings sells them. http://www.bocabearings.com/
I'm not sure if the silicon nitride bearing made much improvement. It certainly did not make the magnitude of difference that changing the oil to Mobil SHC634 did (that's a huge upgrade). I'd recommend trying to get hold of a quart of SHC634 and relube the existing bearing before trying a ceramic ball.