It does not exist. You're far from the first person to find the idea intriguing. But unfortunately 99% of third parties don't make them themselves, they use molds obtained from official manufacturing lines or simply buy time from the same people making official backplates.

Best you can do is a case or a 3d printed clip on.

standard and OLED backplates and kickstand replacements are readily available if you wanted to try making a Frankenstein creation of your own.

https://www.amazon.com/eXtremeRate-Console-Replacement-Housing-Nintendo/dp/B0B4B5DYT1