i think it would be very hard to get an accurate number. i personally have 6 balls, 1 JCP, 1 GTP, and 1 Corn, and they are all "pets". just an example-the guy next door to me might have 80 balls, 8 carpets, 6 GTP, and 40 colubrids, but to him that is his business and he breeds them, so he would not classify them as "pets" to him therefore not registering them, since they are a business to him.
look at just some of the big snake breeders they have 1000s of snakes so i would guess the number is well over 1,000,000 if the breeders would consider them "pets".
and i put "pets" like that because, i consider anything in my house that has a name, if its my dog, snakes, fish, turtle, or anything part of my family so there is no pets in my house.