A seller on eBag has Bushnell parts that may fit this Beeman scope. I just checked and the Bushnell Sportview screw he has listed will fit (I believe) the Beeman scope shown here beside a Bushnell Sportview.
https://www.ebay.com/itm/185018383257?hash=item2b13f47b99:g:vgcAAOSwrjthKAV8
I need one for the RWS Hakko shown here. I tried my Bushnell Sportview screw in it and it seems to be identical. So I ordered one. He also has some other scope parts listed
That cap looks very similar to the Beeman 66x series caps as well. Thank you for posting, as it's good to know if a possible replacement part is easily obtainable in the present day.
The Beeman scope I showed is a Blue Ring 49r. Not made by Hakko. Pretty sure it's a Bushnell Sportview Korea
