BillR wrote:

I can be extremely hard to find tiles to replace ones that are say more than
10 years old.
I've done it by going around all the outlets and asking them if they have
any old stock and even rang the makers, if you can find out who they are.
The modern fashion for all white tiles in bathrooms does make it easy to
source matching ones.
Alt. maybe consider replacing the two rows with a complementary colour

That would be my choice - make it into a feature. You might want to use
the new tiles elsewhere in the room as well, to make it look intentional,
rather than patched in.