One word of advice - until I gave up my shop a few years ago I did a regular trade in framing medals. I found that unless the medals were going to be taken out for wear from time to time (Remembrance Day, etc) it was better not to have them mounted for wear first, as the brooch pin did not allow them to sit neatly in the frame. Better to mount the medals suspended from their ribbons directly on to the backing cloth of your frame.
As far as sources of supply go, I am sure any of the suggestions so far will be fine (and yes Spinks are a bit pricey, but very good). I personally recommend
Worcestershire Medal Service Ltd - Medals, Badges, Mounting, Framing & Regalia, but its just a matter of making your own choice.