Where I used to work, the company provided the technicians with uniforms. The laundry service had a rack where the steel hangers were placed to be picked up. These were really good, heavy gauge wire hangers, so I took advantage of the nearly endless supply. You might ask folks you know that work in a shop, factory, car dealership service area, etc. to see what they can come up with. Maybe even go to a dry cleaner to see if they'd let a few go. Dry cleaners have really stout wire hangers for drapes and other heavy items.
Home Depot also sells galvanized steel wire in 9 gauge (Store SKU # 196248) and 12-gauge (Store SKU # 197502).