Been trying to get a spring maker to make them for me, definitely a market for them. They go flying when most people take them out. Problem is 1000 minimum and a buck a piece! Felt is easy buy it in sheets and use a hole punch on it.
Try a hole punch in a drill. Works slick. Carpet, melts a perfect hole. Push a pick up from below and its dead on. I stopped hammering the hole punch after the first time i tried it. Even heavy gasket material and thick rubber.