The only thing I could find was https://guns.fandom.com/wiki/Heckler_%26_Koch_NBW

I assume caseless is just too niche for pistols - even if you developed it, without a major military adopting it, it just wouldn't have enough traction for anyone to switch from what they're already using it, and for militaries pistols are a relatively low priority weapon so they wouldn't bother with anything particularly groundbreaking