How do I unlock rulers?

I'm so far enjoying this season, although I think single trait will get fairly boring fairly quickly, I appreciate the extra flexibility and I'm glad they're experimenting with new things. All this being said, I'm f2p and I only have the king, loong, the builder and echo sage. I don't know how to get the rest, and trophy road only seems to allow me to unlock tomb queen. I'm particularly interested in the goblin queen, so if there's any f2p way to unlock them, I'd be grateful to know!