You could try TGO, thirdgen.org. Thats how I found the T56 for my 84 TA. Was in the right place a the right time when I got it. Otherwise, Ebay, Hawks, Hanlon Motorsports, or Craigslist is your next best bet. They're out there. Just be aware, you may have to pay.
Heres one in Long Island if all you need is the trans...
http://newyork.craigslist.org/lgi/pts/3392384979.html