The original wet chemical extinguishers were all unpainted stainless steel, the Amerex, the original Chubb & Kidde Thorn Fry Fighter (based on a US Badger water extinguisher) and the Britannia FCC Foam.
Water mist is f rated, but only in red steel cans from the 3 main manufacturers (Jewel, FireBug, SFFECO).
I can see two options, neither cheap:
- Get a 'special' from Amerex where they import an unpainted US Wet Chem model B260 and see if they would put a UK label on it (the US has a green colour code band and refers to class K)
- Ask Britannia Fire if they will manufacture a special.
Check Fire might be able to assemble you a Commander one using the 6 litre water/foam stainless can, filling with WC, fitting the lance and a suitable WC label, but of course there may be fire rating/approvals issues with all these options.
Supply & demand is why you don't see polished WC any more, it's probably the least sold type as it is