Hi Arian,
These place you can buy a single item if you like as I have done, no need to buy meat you won't cook.
Tom Hixson changes all the time so best to check every other day as they have a stall at the famous Smithfield market in London.
I'll have to check the pipers farm link but you can also Google them and look at the rest of the meat they sell.
As for fox holes they are a small local farm that have a on site shop and butchers. I probably should have mentioned with that one since lock down you have to call them. They are really helpful and friendly and you can speak directly to the butcher.
My favourite go to is John Davidson, again it always changes due to stock. I've had a few Wingham reserve briskets from there and after 9-12 hours in the smoker come out incredible ever time. 100% recommend.
Hope that helps.