I know plenty of people have given you advice and it's fairly sound; just figured I'd add my own input as well.

Don't be afraid to bring it up. The first girl I had a long relationship I eventually told her and she let me enjoy her hair many many times. I had another girlfriend who when I told her about it, offered for me to play with her hair all the time and encouraged me to be as rough with it as I wanted.

There was even a point where I had a friend whose hair I really found hot, but didn't want a relationship with. I asked to play with her hair one day and eventually divulged about my hair fascination. She said I could play with her hair any time I wanted.

Don't be afraid to bring it up. I've been in several situations where I've wanted to bring it up, but been too afraid. However, anytime I've asked to play with a girl's hair, or even be sexual with it, they haven't said no.

I think of all the replies, the best one I read was don't make it about the fetish; make it about them and their hair and you will be able to get satisfaction with your love of hair.

Go for it.