You could always add one yourself, through the SM functions. Then if you wanna 'discover' it, you can delete a connection if two between you and the system you put the NPR in.
Try discovering few new systems. IIRC that 100% chance is the chance NPR will spawn on a suitable non-ruin planet. Some systems just may have not enough decent habitable planets.
I'm building a nice a military fleet and i want to do a war with someone, but i can't find anyone. I set the NPR generation for the player at 100 (https://i.imgur.com/B3Wb6Ly.png) but i can't find any NPR.