The black "thing" on the contax g lenses

Hello

I already made a tread where i asked this question, but i did not get any answers so i thought i would try again.

I got a contax 35mm 2.0 that missed the black plastic "thing" that sits on the bottom part of the lens, lens works fine on my contax g but i really would like to get the plastic "cover" replaced since it is a very special lens and right now i got black tape over it as a pretty bad but working solution. Anyone have any idea what i can do? can i contact someone for a spare part?

Thanks for your time