After some long exploration, how do I find a system with populated stations to dock?

Most of the populated space is near Sol. You can direct your ship towards Sol by moving towards the 0,0,0 coordinates on the Galaxy Map. Otherwise you might be able to find nearby populated systems on the Galaxy map by zooming out and playing with the View filters - anything with an Economy likely has a station.

Third party tools work great for this sort of thing. Head to inara.cz/galaxy-nearest, input your current location, and select "Universal cartographics". This will show you the closest station that buys exploration data.