FWB 300-s modern sites

[Richmeister]

Hello,
I'm wanting to find a riser block for the rear site of my fwb 300 s. I've recently fabricated a front site mount for an adjustable iris 22mm front globe.

However the original rear site doesn't have enough elevation and shots are hitting 1.5" - 1.750" low.

Is there a riser block available that will work?
Otherwise I'm not opposed to buying a new "modern" site but would also need to know what one that would be compatible with the rounded receiver of the rifle.
I read a lengthy post about someone with a fwb 2000 rimfire that was up against this similar task but the thread never continued so I didn't find much more information on the subject.
Hopefully there's someone who has done, or knows someone who has done this.
Richard