The click that engages in the ratchet wheel prevents the spring from unwinding. A small click spring pushes on the click to ensure it re-engages on the next tooth. These springs were made in a vast range of shapes and sizes and the chances of finding a new one that exactly matches yours are small. They don't bend easily because, being hardened, they are brittle and will snap. A repairer will normally buy the nearest and if that doesn't fit, soften it gently with heat to allow it to be bent. This will reduce the strength of the spring so it needs to be hardened and tempered again. The only task this spring has is to press on the click, and sometimes one sees repairs that have been made by using a different shape of click spring altogether. This will involve making additional holes in the clock plate, so is not considered appropriate. However for a movement of little or no value it can be a simpler solution.
Repairing Your Own Clocks by Mervyn Passmore