Below you can find a link where they sell a Paper clip and spring on Ebay
This is an affiliate link which means I'll get small commission if you buy it.
Amazing Nitinol (Memory wire) - Experiment
Nitinol (Nickel titanium) also known as memory wire or memory metal, is an alloy between nickel and titanium and can be programmed to a certain shape. When it has been deformed, it can go back to its programmed shape by heating up the metal.