I found this site, Vintage Dogs, that offers great vintage dog stuff. Mostly books and ephemera and postcards/illustrations. I didn't find a ton of Boston Bulls but the site appears to be updated as they acquire items so check back often.
I was particularly intrigued by the Leeds Castle Replica Collars pictured above and featured on their site. These 18 and 19th century collars, originally worn by dogs of the English aristocracy, are repoussé and chased sterling silver. You can have one made for your dog for a few G's, engraving is included (see images below), jewels extra.
If you happen to be planning a trip to england be sure to visit Leeds Castle's Dog Collar Museum. Nearly 100 collars and related exhibits in the Leeds Castle Dog Collar Museum trace the history of canine neckwear from medieval to Victorian times. The page has a brief history of dog collars you may find interesting, especially if you ever wondered how spiked collars came about.
UPDATE!! Check this site out for more collar pictures.
Or see it here: