I just noticed that you haven't gotten any replys on your post. I also have seen those lovely sashiko fabrics but I'm not sure how the quilting vs. sashiko stitching works. There is a LQS a ways from me that has them and the owner was very helpful to explain the stitches, fabrics, etc, but I didn't think to ask about the way to quilt it when done. I think I'll ask her the next time I'm in her shop. If your source is close by, ask the shop owner. She'll know.