I've visited 10 Atlas Interfaces, collecting the stones, and then visited an 11th where I can finish the Atlas path. However, I sold my first stone not realising that I needed to keep them, and so I didn't complete the mission. I've since travelled through a couple of black holes and quite a few warps, buying a 10th Atlas Stone on the way. I'm now at a loss as to how to find another Atlas Interface, as Nada and Polo no longer offer to show me one nearby.
Do I just have to keep travelling and hope I get lucky?
Best Answer
According to this Polygon article, (be warned, there may be spoilers if you read too far into the article) following the Atlas Path will bring you along to more Atlas Interfaces/Space Anomalies. This will allow you to get the stones you need.
However, in your specific case, finding one after straying from the actual path, and without Nada and Polo's help, is really up to chance. As far as I can tell, you'll just need to keep flying through new systems to find a new Atlas Interface. This is just a slight speculation based on what I've dared to read in the article, and from my own experience. I don't want to spoil the game for myself, what with all the information and mystery surrounding the center of the galaxy so unfortunately this is the best I can do.