Hi charlie007,
I'm a fair way through a false chimney build myself and have used a single sheet of mdf for the front of it (thread and pics here -
....and so it begins - my first install, a fake chimney breast). Cutting the spaces for the speaker, tv and feature hole were fairly easy but took a fair amount of planning to make sure they're in the right place for the frame.
If I could do it again I would definately cut these holes out first to be perfectly square to each other and the edges of the board then build the frame to fit it.
Unfortunately I can't help when it comes to any companies to do it for you as I've tackled it myself!
Cheers,
jamesk190