If you are training at an academic program with a university, the student bookstore will often sell them, sometimes with a neat university seal/logo on them (at a price of course). I love mine with the university picture and mascot on it.
Other places are frame stores like Michaels, Frames USA etc. They have a "60% off" sale like every other month, so wait until you see one. Target sells frames with mats that you could DIY if you should so choose.