my stash has mostly come from leftovers from quilts. look to freecycle in your area, to maybe come up with cotton fabrics.
i moderate a board in our area.
i think White fabric or White on white is always needed.
if i have a coupon for Joanns or hobby Lobby, i get a couple yards of "blender" fabrics.
i also try to cut small pieces of fabric leftovers into 2 or 3 " square pieces, and toss them in a box, for scrappy quilts to make at a later date...