Huh so what you are saying is that if you were at a guy/girl school you would only choose girls from that school.
Last time I checked there were about 50% of the population that are female.
I never really spent all my time at school... and I met a whole lot of women outside of school.
Getting a girlfriend is not about school. It's about you. It's about giving of yourself in a way that is attractive to the opposite sex.
So stop being selfish and thinking about what a woman can do for you... and start thinking about what you can do for them. When you do that you will find that getting a girlfriend isn't very hard at all. Chosing which one will be the problem.