Yes, steve23 (KLOV ID) makes repro (steel) "B" gears. I think NOS of most if not all of the gears are available from several sources (Happ, Betson, as well as user Mylstar here on KLOV).
Yes, any 5K pot shoud work (electrically) fine. Not any 5K pot will physically mount and fit properly, though.
hacksaw the shaft down. and tighten the nut down good since there is no notch to fit into the groove on the mounting bracket, but otherwise i've used radio shack pots when i'm out of the proper ones.