Push on scope turret caps.......?????

[averageplinker]

Hi all,
On my project Webley Omega I have an 80's (?) vintage 3-9X32 ao scope by ASI. It is missing the top turret cap which appears to be a push fit as there are no threads. Was this common back then? What are my chances of finding a replacement or an alternative? Do any maufacturers currently use such caps so that I may approach them to buy spares??
I think I may end up improvising but who knows
Thanks in advance for any suggestions

[averageplinker]

......I will be improvising
Night all.