Think your nearest hard anodising place is in Nuneaton, used them a few times up to 14 yrs ago, not cheap either.
They will do most colours hard anodising but what they call gold/yellow is more like mustard colour same with other colours, they look naff.
Can even get ptfe impregnated hard anodising coloured and would only go for black or a darkish grey. All other colours seemingly look sickly.

For a scope sulphuric will be more than good enough as used on 3k scopes.
Many places will have minimum charge, Parkes in Walsall in 94 was 75+vat per colour. You might find one that will do cash but need to go in personally.
Just had some butt pad bits done in Brum today, dropped in at 8am, ready at 12.15.

Havent done any sulphuric anodising myself for at least 8 years, even done a few hard anodising jobs essentially the same with much lower temp.