Hope you don't mind if I tag along for updates?
I'm also trying to get these beuties for my tank for good over 6 months and only came across some old posts on international forums, so would be nice to source them UK home breed.
How's the colony growing @MirandaB ??
I was wondering many times: aren't these snails native for the lakes and rivers in the UK? They live like in thousands in southern Russia where the climate is not significantly different (but apparently taking them from Russia to the UK is not a trivial thing for many reasons). Theoduxus snails, both 'wild' and aquarium bred, are also actively used by aquascapers and other hobbysts there.
They are native to the UK. If you search on the <"National Biodiversity Network (NBN)"> you'll find that they occur all over the UK, where ever you have clean, hard, flowing water. This is southern central England, and you can see the records follow the course of larger rivers.
Regarding some information, I could find about their habitat and ecology, that might come handy if you look for them in nature... As Darrel mentions, they are mainly to be found in strong flowing clean and oxygen-rich fresh but also brackish waters, also lakeshores where the water is moved by wave action. Living on hard substrates such as stones, old shells and occasionally on driftwood.
Considered in decline in Mainland Europe, but still very common in the Baltic Sea area in brackish waters.