Apparently there are bots that can do this, but don't overlook Facebook's own algorithm.
Facebook actively promotes related pages if you have liked a related page or a similar page.
I had a client that went from 10,000 page fans to 3 million primarily because of this "organic" algorithm-based system.
Of course Facebook tends to recommend pages that it believes has greater indications of quality, so fan page engagement levels do play a key role in how actively Facebook would recommend your page to potential fans.