Hi, do you mean Mounts around a print then put into a frame?
if so, I generally cut my own now, I bought a mount cutter from hobbycraft for about £15-20 and its a freehand one so (if creative enough) you don't need to stick to straight lines. It takes a little getting used to but the results when used with a good rule as a guide are easy and as you'd expect when bought over the counter somewhere.
The mount boards are about A2 size and depending upon colour/stockist are about £2.50 per sheet. I buy most of mine from either hobbycraft or Colemans, but I'd imagine most art shops would stock these.
In no time at all (assuming you want more than one) you'll save the price of the cutter and wasted mount board/mat. I was recently in a highstreet picture framers and a woman in front of me had asked for a mount to be cut, 5 mins later the guy came back having just cut the mount and charged her £11 for it. This mount was only about 14" x 16" and a plain cream colour.
Cutting your own also allows you to be a little more creative than a plain mount. I've cut a couple for use with motorsport prints that use 2 coloured mounts joined to match the colours of the bike/car in question and the results have been quite pleasing.
Hope this helps.
