In my humble opinion, it is FAR better to go to a factory or fitting centre than to see if you can get it done locally. Just the choose the system you want, and be prepared to go to their factory for fitting.
Yes it's a bit of a pain, it will probably mean you need to take a day out and perhaps even stay overnight, but i think it is the best way. By restricting the choice of suppliers to those will fit locally, you are narrowing it down too much. The system is the most important thing. In 3 years time you will still (hopefully) be using the system, and the day you took off for getting it fitted will be a distant memory. So if you've compromised on your choice of systems for the sake of 1 day's convenience, you have to live with that for as long as you have it.
If you go to the factory where they are fitting them all the time, they will have everything they need to do it properly and safely, it doesn't depend on the weather, etc, its just a better way to do it.
I got my Pure2o system installed by ionics at their head office in Swindon. It was done quickly and efficiently, including the speedliner, it was perfect. And I've never had any trouble with it at all.
Just my opinion.