The book Underground Railroad Sampler Quilt (I wish I owned it) is suppose to be great. Hidden in Plain View is a book about the underground RR and in the back it has what block was used for what code. Reproduction Quilts has a pattern The Freedom Quilt C1850 inspired by the ides that quilts were used by the underground RR. I check for you it is still in print and costs $9. www.reproductionquilts.com
Hope this helped, I live and breath the Civil War and the years leading up to it. It is proven through written documents that in SC there were indeed Freedom quilts even though people say they were a falsehood. If you go to www.osblackhistory.com/quilts.php you will get a good education in freedom quilts and how they were used by slaves. I wish all who disbelieved in this fact read about it. Also I live by the ONLY Freedom center in the US, they have the only slave pen know to exsist and when I spoke to them a few years ago they have confirmed that freedon quilt were used by the underground RR, however in was in only a few stated. Ohio was the place slaves were headed, there are markers all over the town where I live showing safe houses, conductors etc. There are even mapped out tours of my area it was the runaway slave hub.