I'd have thought you would struggle for a second hand one as most folk who would change them, do so because the original is split/faulty.
Which type do you specifically need as both those you mention use different water inlet connectors on the pump hose. The Truma Ultraflow is available as an upgrade kit with trigger fitting; example here, or there are some reasonably priced inlets only on Fleabay.
Alternatively, as you're in Walsall, have you had a nose in Tent Hire in Edward St? He can be a bit of an "Aladdins cave" for stuff.
I would assume then that you mean the Carver Crystal inlet, something like this ...?
I'm fairly sure Truma didn't produce inlets for your age of van (happy to be proven wrong though).
If you have one of these which has a problem, then I would recommend the Truma Ultraflow conversion kit. The Crystal inlets weren't great and you couldn't guarantee a second hand one was any good and free from frost damage.
mine was similar to that,those horrible lugs that broke and were impossible to turn,simply replace it and upgrade your pump fitting to the pistol grip type.Its not expensive and the new housing should fit exactly where the old one came out,it took me 30 mins to upgrade mine.