Recently we have seen a lot of people on Liothyronine (T3) having to contact pharmacies in their areas in order to track down a supply. On previous occasions, we have seen the same need in relation to other medicines.
The NHS is well aware of this need and has produced a way of finding local pharmacies (or other NHS-related services). Go to this link and enter "pharmacy" and a location, e.g."watford":
You might have to click a couple of times, but eventually that gives you this page:
In my limited experience, the list has been accurate. The same search mechanism is able to locate various other services/providers.
Also, the NHS site has an Internet Pharmacy list: