This tutorial on Spoonful.com by
Goodwill Outlet Store in Appleton, Wisconsin that offer textiles and other materials at a flat rate per pound.
-Freecycle "want" posts: Since old clothing IS something that will often end up in a landfill, it's something perfectly rational to ask for. Be forwarned though, practice good judgement when meeting other Freecyclers to pick up items. Most Freecyclers will leave their items out on their front porch/in their mailbox/by their front door for pick up. Entering a stranger's home is unwise.
-Group sourcing: While this is obvious, I'm going to mention it anyway. Let your co-workers/family/friends/etc know that you're collecting old shirts. If someone gives you a ton of discarded shirts, a nice "thank you" might be a rug of their own.