These are bases for a Austrian "Wiener Schnaeppermontage" = Vienna style snap-on-mount, often called "Springer mount" after the well-known Vienna gunmaker, see the drawing from Lampel/Mahrholdt:"Waffenlexikon".

These mounts were quite popular in pre-WW2 Austria, but obsolete by now. They are often seen in a three-legged version on Mannlicher-Schoenauer rifles. More often than not they were used to mount 2x or 4x Austrian Kahles steel tube s copes, using soldered-on half rings. Little hope finding a scope and rings to fit your bases, as these mounts were apparently handmade by individual gunsmithes.
Here are two 4x Kahles scopes with such mounts for Mannlicher-Schoenauers