Have you tried ringing round all the petshops?
Big petshops aren't always good for gerbils (as they often aren't handled well and you're never quite sure of their breeeding) but they may know a breeder who's selling some.

It's a personal opinion, but I find female gerbils nicer also! Males are still friendly, but I much prefur females!

But good luck, gerbils are lovely rodents to keep.