Searching patents will likely help a lot. I'm using US patents here because they are easy to search (and for me to read); some of these were patented a few years earlier outside the US.
US Patent 3195432 to J-M Baluteau of SOMHP (France) seems clearly relevant, showing what a reflex viewing system with what looks like a microprism screen:
https://patents.google.com/patent/US3195432A/en (1965, original French patent 1959).
They cite a previous patent US 2969706 to Rosier and Baluteau
https://patents.google.com/patent/US2969706A/en which doesn't seem to use microprisms, but it does cite an article by Dodin, "Focusing with Crossed Prisms" in Amateur Photographer.
There is also cited the earlier US Patent 2986599 to Lindner and Kosche
https://patents.google.com/patent/US2986599A/en showing a microprism screen in an electronic (TV) viewfinder. This patent cites Dodin
https://patents.google.com/patent/US2669916A/en , which is clearly a patent for a split image rangefinder (but not microprism). Lindner and Kosche refer to their own article "A New Optical Rangefinder for Television Cameras," in Nachrichtentechnik 1956, No. 12, pp 538-544, so now you just need to find some back issues of Nachrichtentechnik (literally "News Technology," but as I'm sure you know better translated as telecomms engineering).
I got to the Baluteau patent by tracing patents referred to and cited by through several patents including:
https://patents.google.com/patent/US2589014 to McLeod of Kodak, which is clearly earlier but describes a sort of screen made up of cones, not wedge prisms.
https://patents.google.com/patent/US3003387 a Rollei patent for a screen that combines Fresnel and focusing surface onto a single surface.
https://patents.google.com/patent/US4352547 a much later 1981 Nikon patent for a method for optimizing the microprism wedge angles.