have you an address in bridgend of firm who can install simple air suspension to my hymer
Welcome to MHF. If you are talking Bridgend in South Wales then I'm not aware of any specialists in the local area.
Having said that, the fitting is not overly complex and I (like many on the forum) have DIY'd it. If you (or a friend) are reasonably competent with a spanner and a few basic tools then you could consider just buying the kit and fitting yourself.
The very first time I had it fitted on a van I used http://airide.co.uk/
They are based on the south coast but I met them in a service station on the M5 and they did the job there is about an hour or so. They also attend many of the big motorhome shows where fitting can be done.
If you want to speak to a caravan/motorhome specialist then I'm happy to recommend Automaster in Llanharan. I don't know if they've done air suspension work but they have done habitation work for me and I've been very happy with them.
P.S. All the above assumes your van is built on a standard Fiat/Peugeot chassis. If your van uses an Alko chassis then the process may be more complex.
P.P.S. You may want to edit out your email address in case the spambots pick it up. People can reply to you in the thread if they do have any recommendations.