This article is from the American Pit Bull Terriers Breed FAQ, by Michael Bur with numerous contributions by others.
A good place to start looking for APBT related supplies is in the APBT
Gazette. Below is a list of a few places that sell APBT related supplies.
This list is by no means exhaustive.
17501 East Main
Galliano, LA 70354
Newman Leathers makes an assortment of leather collars and harnesses.
I don't know anyone who has purchased anything from them, but the stuff
looks impressive in the catalog. Owners of other Bull/Mastiff breeds
may be interested in their collars.
HC 67, Box 117
Bruno, ARK 72618
These are the same folks that put out the Bulldog Review. A whole
assortment of collars, leads, books, you name it. A good source
for the older, out of print books listed in this FAQ.
Iron Pit Kennel and Supplies
25386 Bunker Hill Ct.
Hayward, CA 94542
They have a catalog. Sell misc. collars, leads, etc.
Also make and sell spring poles and Treadmills.
T. & E. Miller
317 Old Morgantown Rd.
Bowling Green, KY 42101
They have a catalog. Sell misc. collars, leads, books, etc. Also
sell vitamin supplements and Treadmills.
424 B Gorham Rd.
Scarborough, Maine 04074
They sell collars, leads, books, etc. Also has collectables
and old magazines. See book section for their book.
P.O. Box 793
Meridian, Idaho 83680
THey have a brochure. They sell collars(obviously), leads,
Bell Dog Leather
P.O. Box 5606
Pittsburgh, PA 15207
They have a brochure. They sell collars, leads, harnesses,
tie-out hardware, books, etc.