In our area there are a lot of thrift shops. These are wonderful places to look. I've pulled cotton blouses and dresses (with tags still attached) for just a dollar or two. Lots of good fabric. Garage sales and auctions bring lots of neat fabric into my stash also.
The word has gotten around that I "accept" scraps so get bags and boxes of scrap. Go through them to see what I can use then pass the rest to church groups who do quilts etc -what they cannot use goes to a "rag man" who somehow uses the fabric for grease rags etc. Not a lot wasted.