Welcome to the forum Jack.

I can certainly sympathise with your plight, the number of species available to us in the UK is limited. We've been lucky in getting a couple of less common species because we got connected with one of the other UK guys on here (actually my wife first contacted him via RFUK) and JohnC had been to Houten and Hamm this year and decided not tuo keep all 4 cuitzeoensis that he had, and later the person he brought a pair of Western Blacknecks back for decided not to keep them. So we got lucky by getting to know someone 45 minutes drive from us who had brought snakes back from Europe.
Its going to be another year or so before either of us start seeing babies out of out current snakes, but when they do breed it will increase the number of rarer species available. There are a few shops in the UK that occasionally have stock of garters, but generally they dont bring in anything tooo unusual. There are a few other UK owners that breed and post on here, although the only unusual morphs I'm aware of recently available aresome melanistic Easterns (you could try PMing Scorpian to see if he still has them).