If you sell pimps, what does that make you? A pimp pimp?

No, It would make you a Pimp seller. You would only be a pimp pimp if you rented out your pimps for an hour.

could you still be arrested for pandering if you sell pimps?

I think the term is "pimp's pimp" and it means you're highly regarded in the prostitution industry -- "See dat guy? He's a real pimp's pimp."