User blog comment:Omega natsu2/Chapter 371: Tartarus Arc, Part 2: Song Of The Heavenly Dragon, Predictions./@comment-198.142.230.136-20140210052414/@comment-7418318-20140212091313

There were a lot of unnamed spirits when they visited the spirit world, so there most likely are a whole load of keys around the world too. 88 constellations (plus snake), some of them even with multiple individual spirits (like Canis Minor).

But who said Lucy has to possess all of them, much less carry all of them with her.