HMMMM. I have no idea what a quilting mat is, even though I am into quilting somewhat.
Are you doing bc or fondant?
If you're doing bc, I read you can place a vinyl tablecloth over your cake (one with imprints or ridges) and press to get the effect.
If you're doing fondant, you could use a fondant roller w/the decorative "blade" to get that effect.
Are you talking about something like this?
http://www.earlenescakes.com/store/impression_tools.html (Scroll down to the middle of the page.)
I bought my matts at the convention, but I know I paid $5 for it. I haven't ordered from her, so I don't know about her shipping or anything else. But if you look around on some other cake supply sites you should be able to find it other places as well.
I haven't used mine yet, but may this coming week.
Quote by @%username% on %date%
%body%