I had a similar issue - my PS was setup in the UK and I no longer had a UK card..
I bought UK PSN cards from here:
https://www.play-asia.com/search/sony+psn
The advantage here is that you can pay for them using any credit card - whereas if you try and buy UK PSN cards from UK Amazon, then you still need a UK credit card / method of payment.
Have bought a number of cards from them - you usually get the PSN code instantly - sometimes takes a few minutes, and they you can just add it to your wallet on your UK profile.