Gas Valve seised on Gas Fire

I'm having trouble with the Gas Fire in my living room, would love to have this working for Christmas, so any advice would be much appreciated. We built a house in 2009. We bought a Gas fireplace from Gavin Scott Designs it has a product code of GSD890, there is information about it on their website but I can't post links.

It was installed and fitted at the time by the builder and his plumber. The Gas fire part of it worked for a while but stopped working at some point. When I was getting my boiler serviced I asked the gas service engineer to look at it and he
reckons it's the gas valve that is broken. The switch to the right is completely seized and will not turn at all.The details on the insert are

Diamond Super Model DF 16" NG Serial No D1090.

There is another code on the valve itself:
GV34 -C5AODVKL-0001
CE 0085AP0169
4/9
The product has a remote control.


I've googled and it seems to it seems to be a Mertik Maxitrol part. I can even find similar ones to buy online, but am afraid to go ahead and order one, because I don't know who to get to fit it, and I'm afraid I'll buy the wrong part.

Would anybody know if you think I would be able to get the existing gas fire fixed or source and install a new one that would fit into the existing fireplace?

Who generally does this type of work, I've e-mailed both the fireplace businesses in the town I live in (Dundalk) but no reply from either.
Thanks!