I've just ordered some pots from Blore Edwards
https://www.blore-ed.com/potentiometers
Proper vintage style and they do imperial sizes and custom jobs too. Fast and friendly service from Brett and Amy.
The prices are very reasonable. Postage seems to be a standard six quid so for one pot it's a bit expensive but I have several projects waiting so it made sense to order them together.
Highly recommended.