Probably the most knowledgeable person in the world today on the
subject of hide glue is Mr. Eugene B. Thordahl, who has a company
that can be found at

  Bjorn Industries, Inc.
  551 King Edward Road, Ste: 211
  Charlotte, NC 28211
  tel.: 1-704-364-1186
  fax:  1-704-364-1098
  email: info@bjorn.net
  http://www.bjorn.net/

His price list includes glues at 11 different gram strengths from
135 to 444 (the latter used for chipping glass).  Lots of information
available as well.  He lists discounted prices up to 50 lbs. but invites
requests for quotations on larger quantities.  I've been using this glue
in the 192 gram strength and been very happy with it.  The couple of
things I've had to take apart after gluing with it suggest that it is
very strong indeed! My luthier friends swear by this stuff.

Cheers!
Roger Wiegand
Wayland, Massachusetts USA