Sorry FighterFish, you are in the wrong part of the world for me to help. I ma a wild type endler breeder who is registered as such in the US.
Have you tried asking on the British Livebearer Association site yet? The forum might be considered by some as one of our competitors, but any forum with that little traffic is no threat to us. It is a place where livebearer specialists may be able to help you connect with others in the UK. I am a member and participant in the American version of a livebearer association and find that things like finding endlers are almost a trivial exercise for our membership. The BLA is a sister organization that should be able to help you if you are willing to join them. At the very least they will be able to connect you with club auctions where you may find some great buys on hard to find fish in the UK.