Does anyone know where I can get a pattern for those microwave potato cooking bags I've seen at craft fairs?

Google Microwave Potato Bag Patterns and you'll get plenty.

fabric depot has the pattern. they also sell the warm tater batting for it. they were the cheapest i found. when i got mine it was $2 a yard (22x36) now it is up to $2.49 i made about four or five so far, i started using mine last week and i love it! just be sure to use 100% cotton with everything - fabric, batting and thread! also just as a side note my sis went to the quilt show in columbus ohio last weekend. they were selling the kits but she had a hard time finding the tater material by itself. a big thing now is corn bags. according to the directions on the pattern you can use it for corn also as well as heating up dinner rolls. so don't limit yourself to tater material. i made some red green and tan striped and they turned out beautiful!

I just made a couple myself. I got the Tater batting from JoAnn's. One package will make 6 bags. I googled potato bags and found many patterns. I read them all over and combined a few to make my perfect bags. I haven't tried them out yet though.

I will surf and see if I can find some free patterns for us

go to the warm and natural website. click on products (last one) is warm and tater. there is a pdf file for pattern

I have kits with the potato fabric for sale!

They ework great but be careful, friends caught fire, I used the tater batting and tater fabric. I had heard of it but figured they used wrong fabric or something. I still use mine, just dont leaveunattended. Friend asked for another,so she not worried either. Have heard cob corn good, too. Cant wait to try it.

Its posted on the Warm & Natural Site.
Here is the link to the English PDF file.
http://www.warmcompany.com/WarmTaterPattern.pdf