New TM owner with questions.

Howdy all!  Great board and info around here!  Spent 6 months  looking for a decent used TM and found and bought a 1994 3124 in RI.  My ? is: how do I go about ordering parts direct from the factory?  I want to replace a couple of roof vent/light units.  Dealer in Cape Cod  says they can't get direct replacements as parts are not made anymore.  All the vents I looked at have a fan and light.  I want just a light in the vent.  Anybody know a source/  Thanks much!