You might try the local hotels and motels also. My experience has been that there are usually several blankets or comforters that have been damaged or stained and they are unusable for customer rooms BUT they are still very usable to any person who needs a blanket. I used to give those blankets away to needy families when I ran the motel.
ALSO franchise hotels/motels are required to replace their blankets periodically and would probably be more than glad to sell them to you fairly cheap - especially if its for a good cause.
ALSO there may even be several blankets and other items left in the lost and found that have been there for years. We had coats, blankets, shoes, clothes, ice chests, backpacks, duffel bags, etc that had been stored for years. We were only required to hold them for 90 days and then they were supposed to be discarded. Again, I passed them on to needy families.