Ask around. Springs may be found at hardware stores, bike stores, and espe- cially junk merchants in markets. If you tell some of these people what you are looking for, they will probably find it for you by the next time you come to town. There are also much thinner springs readily available at stores that sell window blinds. There is a small white long (1 meter to 2 meters) spring used to hold up window shades in homes. Use a knife to remove the plastic coating. Cut the spring into small segments and you have 10 to 20 5 cm long springs with a useful spring constant.