Try Aquabid. There's loads of eggs on there but also fish. I've had fish delivered from as far away as Germany. They are very easy to raise from eggs as well though and then you'll get a small group rather than just a pair.
Shame you missed the "BIG ONE". It's an auction in the Midlands (Redditch), loads of stuff there. If you join the BKA you can go to their convention in St. Albans (Junction 1 of the M1). October I think it is.
I got some Epiplatys annulatus and Epiplatys Dageti "Monrovia" in the midland auction and there were quite a few lots of non-killis as well.
I've never used aquabid, but there seems to be an increasing problem of things never turning up that you've paid for.