POP Series print runs?

I’m curious if anyone might have insight into the print runs of the POP Series sets vs. regular sets. I’d also be curious if there’s some consensus on which POP Series sets are the rarest/most common.

I’ve been trying to find certain POP Series cards and it’s been extraordinarily tough. It seems safe to say that the print runs were less than that of normal sets, but these weren’t limited print run sets, right? In particular, I’ve had a hell of a time finding a POP Series 4 Sceptile as well as several other random rares…