I recently bought a box of fabric from a lady who was doing the same thing.
She advertised on our local Kijiji forum - it's kind of like Craig's list but mostly for local things.
She advertised like this.
"Great deal for quilters and sewists. Must destash. All fabrics on sale for $50/box, you choose what goes in your box."
Then when we got there - the boxes were huge! We got to choose our box and fill it with whatever caught our eye - for me it was cottons of course. The box was 2'x2'x2' - when it was full her husband had to take it to my van because I couldn't lift it.