I don’t believe the UK has grown any pearls in centuries. Best
quality pearls are usually vended by Mikimoto, but from what I
understand they are never sold loose, only in thier own jewelry. You
can get probably around this by salvaging old necklaces from estates.
If you want to buy high quality, fresh fish, you cannot buy frozen
from your local supermarket, you have to buy direct from the source,
and if you want good prices: never buy retail.
Most high quality goods, I have learned, behave similarly.
Andrew Jonathan Fine