A couple options....
https://www.newenglandcustomgun.com/Gun_Services/Special_Scope_Mounts.asphttp://www.wattswalnut.com/ms_scope_bases.phpI have also managed to locate Paul Jaeger & Griffin & Howe side mounts on Ebay.
Also the Baush & Lomb/Kuharsky type pop up from time to time too.
I still have a Leupold "Adjusto" mount on my 1950 carbine and will most likely change it out to the Jaeger side mount at some point in time (I have the Jaeger mount already).
The largest challenge is the modern scopes have much larger eyepieces than the vintage units. On the Leupold "Adjusto" mount I had to use various precision arbor spacers to get the bolt handle to clear a nominal Leupold 1-5x20 90's vintage VXIII scope. I want to put a Zeiss Conquest on the gun in the future and will definitively have to go with a different mount.
Good luck!