I'm not really clear about the whole "not mentioning competitors" rule but:
The keyboard company has 104/105 keycap set (blank - black). Blank white you'll have to import. QWER keys is also UK based, but they don't really stock blank keycap (they sell gamer pack (WASD + 4 arrows + esc) in different color though, wouldn't hurt to ask).
If you only want to replace those 8 keys, and not willing to get the whole set, you'll have to import them. PBT blank sets are quite cheap anyway.