How are you getting on with your site? When I was organising the UK MODX meetup last June, many UK developers were no longer using MODX.
That said, there’s a few agencies:
GEL Studios in Swindon run by Graeme, Addido in Winchester, Maple Design in Hampshire.
And a few individuals: Keith(Buckinghamshire) and Simon (Cambridge) came along and there’s me (Julian) in Brighton.
You could likely contact Simon or Keith via the meetup group chat: MODX UK | Meetup
However, everyone else as you’ve seen is very helpful 