I recently did quite a bit of research to find something to meet my needs and never came across side cameras. In the unlikely event that they exist, you couldn't use them for long without draining the pathetic 12v auxilliary battery on the NX 450h+. Other threads on this forum give many examples when the 12v goes flat quickly and I hate to think how long it would (or wouldn't) last in a full 'surveillance' mode. Hell, I get nervous switching my dash cam to parking mode for a hour visit to the local supermarket! There is a fail-safe voltage that is set but that, apparently, doesn't always work (not tested personally).
Sadly, I suspect that your search will bear no fruit. But if you do come across something interesting, please let us all know.
Good luck