Just do a google search - here's the first one I came up with
https://www.gunpartswarehouse.com/CZ-52-Extra-Long-Extended-Slide-Release_p_17.html using the search "cz 52 extended slide release."
Personally I don't see the need for it as the CZ 52 is easy enough to release the slide, plus, it ruins that nice, flat profile of the gun.
Yes, you can safely fire the lower powered 7.63 ammo *HOWEVER* if you've got a strong recoil spring the Mauser ammo might not be able to reliably cycle the gun resulting in all sorts of fun jams.
I got my CZ 52 back in the 90s when all you could get for them was the military surplus ammo and never had an issue with it. They don't make different ammo for the SMGs and the pistols - it's all the same - the stories you're hearing about the military surplus ammo blowing up the gun are likely people using the CZ ammo in their Mauser as the Mauser can't handle the military surplus 7.62x25. Remember, the Mauser 7.63 ammo tops off at around 1400 fps while the CZ 7.62 starts at that and can clock as high as 1800, but usually averages out around 1600 out of the pistols.
It could be possible that someone tried reloading the stuff and made it too hot, although with how hot the military surplus ammo is to begin with it's hard to imagine making it any hotter - I guess maybe use C4 instead of powder. ;-)
To tell the difference between the three types of ammo, just grab a magnet -
Magnetic case and bullet - original military rounds - hot and corrosive - clean immediately after use.
Brass case and magnetic bullet - military bullets reloaded into brass - may or maynot be hot and may or maynot be corrosive.
Nothing magnetic - modern, commercial rounds - not the least bit hot and usually not corrosive.