I buy my mats and dies through a Yahoo group, pinsandneedles. If you go to yahoo groups and do a search for pinsandneedles, you will find it. There are two, obviously you'll want the sewing-related one, lol! You do have to send an e-mail request to join.
She sells mats and dies for 30% off if you are paying w/ credit card or debit, 35% if you pay by check. Can't beat it, and her service is great.
I just finished a top with the 3 1/2" tumbler in springy colors (started 2/ Oasis from 3 Sisters and added to it). Love it. Fun and cheerful! It is a lap/throw size, so I am planning to try to quilt it myself to save money. Which basically means it will be sitting for a while as I am scared to do it!