I love Shibori Dragon for supplies including easy kits. Susan Briscoe is an amazing quilt artist and sashiko expert. She has several fabulous books. I just bought her general quilting book today, 200 Quilting Tips, Techniwues, & Trade Secrets. It's very accessible to the beginner but not boring to the experienced. She also wrote The Ultimate Sashiko Sourcebook, Japanese Quilt Blocks to Mix & Match (pieced, appliquéd, sashiko), and Japanese Taupe Quilts. I get frequent sashiko tutorials free from Studio Aika. Sorry no links :(, hard to achieve from iPhone. Adore Kitty and Sylvia Pippens books and designs also.