My sister has trained my BIL and his son to call us if they find fabric at auctions. Most of the time, it's ok quality fabric, but sometimes its turned out to be quilt shop fabric. However, if no body is interested in clean bolts of fabric, they get it for a buck or two. What we aren't using will go into my garage sale this Spring to give someone else a great deal.
Thanks for mentioning the double knit for quilts. Yes it is warm. My grandmother made a top of double knit with scraps left from clothing making and it is very warm. I'll have to find a local church group who needs fabric for such quilts. Until we're done with this remodeling, I'm just focusing on quilts for me and family members.