I noticed that Step was so nice to make some Post-it-Holders with my tutorial. She asked for some other sources to get to the coasters.
I got mine trough a share on SCS.
An other source is:
American Coaster they should be the cheapest.
http://www.americancoaster.com/ You have to call them though for the blank orders. For the medium weight 4x4 coasters you get 1080 for $15 and change. Then if you want a heavier coaster, they are like $16 or $17 for 980.
Your contact there is email@example.com She is really nice, helped me with all my questions. Be aware that the ones I got worked perfectly with the new SU 3/16" corner rounder. I was over joyed about this - you just cut your paper 4" x 4" and punch the corners and you're ready to rock!
or you can try ebay
(http://www.starlitstudios.com/). She is a well know girl from SCS. Her prices are good, her service is amazing, and she has the 4x4 coasters, 4x6 coasters and circle shaped coasters.
Hope this helps