My observations from the boys system may not hold true by girls, but for what its worth…
No one wants to be used. A good teacher/Rebbe will make himself available for a student when approached, if they see that there is a sincere need. If you’ve approached one with a problem, or desire to discuss something, and been rebuffed, that’s no good. But you haven’t said that. Rather, you feel you may need them in the future. So you want to get to know one, so they’ll be available when necessary. I agree that you need that, but I’m sorry, I think its a disrespectful way to approach someone, and I think teachers sense that. Its fake and insincere. Not enough that you want the person to give time for a relationship clearly one-sided from the beginning. If they got the feeling that you really felt you’d grow from it, that would be incentive enough to give their time. But if you really don’t desire it at all, but want them at your service at some future time of need…
A more sincere approach would be to realize that while there may be times in the future when such a relationship will be crucial, it makes sense that its probably very beneficial now as well. So do some introspection, and realize in which areas in your life you can benefit from guidance. You sound like a mature enough teenager to realize that having the perspective of an older person you respect is always helpful, not just in times of crisis. Then you can sincerely approach them and initiate a discussion, and they’ll hopefully be open to it.