Hi, I really appreciate your attitude toward the recycling of garments. If you let people know that you will repair and donate their no-longer wanted or needed clothing, you would be surprised at what you get. Someone in your area will appreciate the savings realized from play clothes for children or casual wear for the adults.
While I have no suggestion for spools of thread, you might try this for handsewing. If you get your hands on a garment you can remodel and wear, especially dresses and fuller skirts, try to carefully draw lengths of thread from the side seams and hems. This won't work for all garments, but since you have to open a seam anyway might as well try to save the thread for attaching buttons, basting and rehemming. Cordially, Nehmah