I love them too. I've seen them at quilt shows - expensive IMHO. I've received them as gifts and love to use them.
I make my own to give with quilts. I take a picture of the quilt with my digital camera, print it & glue it to a blank card. I write my message inside. I put a picture of the back of the quilt on the back of the card. If I could figure out how to print the picture on the card, I'd do it that way- but when I've tried, I've failed dismally - LOL.
Actually, these cards PLUS having a picture for my quilt album are the reason I asked DH to give me a digital camera for Christmas many years ago. I usually finish a wedding gift quilt at the last minute and never had time to have a 'regular' picture developed.