I got that circle fabric at Joanns, but had to look a long time for it. I thought the cutest stuff was in the quilting section, but most of that is 100% cotton, and not always ideal for every project.
The prettiest/best quality fabrics I've seen are at my local quilt/heirloom sewing supply shop.
This
line of fabrics looks great, and their website gives store locations.
ETA: I second the Amy Butler fabrics!!