Sales, auctions, garage sales.
Once went to an auction where there were 96 boxes of fabric, I'm not talking shoe boxes, but big boxes. I ended up with 19 boxes and after measuring ended up with 2,000 yards. Some of the pieces had the sales receipts in and the fabric was from 1926 - 1955. Found out that the lady who built the stash had worked at the local 5 & 10 cent store. She would buy the fabric on clearance and anticipated sewing and sewing when she retired. She retired and then became ill and passed. Her sister then kept the fabric until they passed and it was sold. If I had known it was all in very good shape would have bought more boxes, but was afraid it would be fraying or rotting. It wasn't, it was all in A-1 shape. Have had a ball using it and still probably have about 1/4 of it left. Shared with my quilt friends too. So we all had fun with it. Lots of charity quilts from it.
Oh forgot it came out to 10 cents a yard.