I volunteer at our local Senior Center with a group of ladies who make quilts to raffle off to benefit the center programs. Our biggest source of fabric etc. are members of the center or their families. When someone passes away or downsizes they or their families donate their craft supplies of all kinds to the center either to sell or use for the benefit of the center. We have a 10'x10'closet at the center with floor to ceiling shelves full of fabric, yarn, thread, batting, and other various quilt related stuff. I am currently assembling a quilt top from blocks donated by a member or their family that will be our next raffle quilt. The one we have currently on the frame was made from blocks donated by another member or former member.
Don't forget to contact church groups.