Justabitcrazy is correct -- Joanne's has it but so do some LQS. Nancy's Notions has it here
http://www.nancysnotions.com/product...by+the+yard.do . This has been used to make the water color quilts, wreaths and other patterns (very popular a few years ago). Adds some weight to the quilt, but the result is really nice.
I have seen both straight and on point grids depending on what you want.