Mountfield RV 150 ,fan vane throttle adjuster broken?

If you remove the fuel tank you can see a black flimsy vane that gets blown out as the engine revs, this adjusts the throttle some how or it would do if the end hadn't broken off. I'v made a replacement out of metal (didn't want another plastic one that would break when it gets old and brittle) trouble is, its to heavy and doesn't react like the lighter plastic one. Can I buy another replacement? how much and where from.
Any help please. Many thanks.