I recently changed all my TRVs because one was leaking, and the design is no longer available. They were the type that Homebase sold - they have a
*male* bush which makes the compression fitting to the pipe rather than the usual female nut.Some were much newer than others, had no leaks and were working perfectly. All the heads were fine too. So there are five perfect ones and 10 heads. Rather than throw them out, anyone can have them for free - either collect or pay the postage - probably about 3 quid for second class parcel post.
However, they're only suitable as replacements for existing similar ones as there's no o rings and they are a special design I'm not sure can be bought these days.