Military tailors in the square in Bulford (I assume their still there) or John Lodge in "Castle Gallerys" Castle Street Salisbury, it looks a run down type shop dealing in coins and medals but John is a top bloke who did a very good job mounting my GSM.
Sent mine off one day, back three days later, cheap as chips too. Fees depend on how many medals you've got obviously - Â£4/medal + Â£5 postage back. Nice job they did too, buffed the medals, replaced the ribbons. and did a good job on the layout and finish.