if you're looking to join a subculture that is long hair friendly other than metal or hippie ones..
Long Hair friendly subculture
Hi(gh)!
Yes, I've seen goth/dark wave guys with awesome long (mostly black, or dyed) hair - but on the other hand, this scene is not very beard-friendly, as the dominant type of longhair there tends to be androgynous.
However, goth/dark wave music (in a broad sense) can be awesome - ever heard Wolves In The Throne Room? In my younger days, I was part of a goth/wave oriented highschool clique, among them, The Cure, Sisters of Mercy and The Mission were absolute musts...
When asked for a longhair- AND beard-friendly subculture, I would prefer Linux programmers! Which have the advantage that they are quite age-neutral, it doesn't matter if you're 20 or 70, while a 46-year-old goth would be somewhat weird...
See you in Khyberspace!
Yadgar
Now playing: Forever Young (Alphaville) - how fitting!
Another would be cruising sailors and liveaboards, especially in the tropics. Easily one of the most open and diverse subcultures I have ever been a part of. Literally, nobody cares what you look like. Its fantastic.