Your LQS might not sell scrap bags but you could ask if they might know of a customer that might have some they would like to sell or trade. Also if your grocery store has a free info board for customers to post notices you could put up a card stating you are looking for scraps.
Also check out the local thrift stores. These items are often donated. I have even purchased some garments as a source for stash fabrics.
Good Luck!