Just bought a holosun hs507c v2 but need a mounting plate. Had a vortex venom but plate didn’t fit the holosun. Anyone know of a plate that would fit?

Hey all, I recently purchased a FNX 45 Tactical via private party transfer, but the previous owner lost one of the mounting plate. I want to mount a Trijicon RMR RM07, but unfortunately that was the plate that was lost. It does not look like a sight mounting kit is currently available...