I have put way too much thought into this. When the brain was working too hard I came up with things like 'an assembly of fabric assemblers' or 'a block of blanket builders', but how awful. 'A gather of stitchers' wasn't so bad, but then I heard about a 'brace of dentists', 'a balance of accountants' or 'a stack of librarians' so I decided that my collective noun contribution would be:
'a stitch of quilters'.
We
stitch the blocks, then we
stitch the quilting, then we come to this forum to get a
stitch in the side from laughing. There are some great ideas here.