There is no real substitute for hops.
However there are many alternatives
Try doing a search on gruit which is the common term for unhopped beer. Hops was a recent change to brewing practices and many other local herbs were used to flavor hops in ancient times. A few are still used in limited brews.
Common herbs include:
march rosemary (not garden rosemary)
I intend to make a couple gruits this spring (if I ever get the time). One using heather and another using mugwort, and sweet gale. If I ever get these made I will update my results.