I have owned ferrets for about 9 years and am a human er doctor.  Based
on your description, I think your ferret may have a spinal cord injury
or fracture.  if not done already, please have him X-rayed immediately.
I wish you luck finding a ferret vet.  You do not state where you live,
but my advice is to get the yellow pages where you live or the nearest
big city and start calling vets.  Ask each one if they have much
experience with ferrets and if not, do they have a vet they can
recommend.  You should be able to get at least one referral to a good
ferret vet- if more than one of the vets you call recommend the same
person then you can be fairly sure s/he is competent.
 
The inability to urinate (and defecate) can be a sign of a spinal injury,
as can incontinence of urine or stool.  I think this is pretty urgent.
The grinding of teeth is often a sign of an ulcer or obstruction (such
as from ingesting a rubber eraser or something that gets stuck in their
intestine).
 
I hope this helps.  My thoughts are with you!
 
Stephen Cox MD
[Posted in FML issue 4600]