It's hard to remember but it seems like there were 3. The two I'm sure of are a recent mutant petpet brush and a faerie PB 3 or 4 years ago, before it was retired. I think the 3rd was a Lost Desert brush that I used to paint one of my aishas.

One of the odder "finds" was when a cheap, common item (what was it???) morphed into the white petpet PB. I just happened to be looking through the SDB when this happened and immediately bought 15 or so. I then painted a herd of hoarded Christmas Doglefoxes that were advent calendar prizes and sold them.