The best places are:
1. General Merchandise stores - Target & WAl-Mart etc.
2. ebay - save on shipping and group items together
3. Graphic Designer / Magic Houses - big places like HOPC. Ellusionist, CARC, Kings Wild etc
4. Periodically check kickstarter - always a good place
I have a bunch of great tips and link in my video: WHERE TO BUY CARDS