You can find a group local to you by searching under groups on Facebook for ‘fabric destash’.
Most quilt shops, either in shop or on their online store will have a clearance section for remnants, off cuts or bolt ends (sometimes called bale ends or roll ends too).
These can be either half-yard or fat quarter bundles usually made up of clearance fabric that needs to be moved on to make space for new stock.
It is the result of overproduction of a particular line of fabric or sometimes small errors in the fabric printing that makes it unusable for its intended purpose.