My parents have one. To our knowledge, Cormack does not specifically have a coat of arms, rather it's from our Buchanan clan. We also have several specific seasonal plaids. I know that they found the coat of arms in an irish store. I'll try to find out more info and follow up on where you might be able to order one.
In the meanwhile, I'm trying to confirm something one of my professors said years ago- that Cormack means Son of the Lionhearted. Any knowledge of that?