How do I locate the rockstars at my university, so as to establish a relationship and get references from them? I'm an undergrad with hopes of entering academia. My transcript isn't stellar, and the general sense I get is that I can make up for this with good references. How do I find which professors have the best reputation, so I can try to establish a relationship and hopefully get references from them?

If the subject is relevant, my area is mathematics.
Every university instructor is a potential rockstar in terms of their ability to help you in your studies, and in terms of their ability to influence an admissions committee.

So, how do you find your personal academic rockstars?


Consider the instructor of every single class you take as a potential rockstar.  Visit office hours.  You don't know whether the instructor will give you extra help, or whether the extra help will be targeted to your needs, until you try.
When choosing courses, look for courses where other students say the instructor is highly effective.  Here are some ways of collecting opinions: visit the drop-in homework help room.  There you should be able to find students who are a bit farther along than you, who can talk freely about who are the best instructors in the department.
Try all the tutoring options at your school.  Some are better than others, so don't get too frustrated if your first attempts don't work out very well.  Try any and all options.
Don't be afraid to look at ratemyprofessor.com -- but do take what you read there with a grain of salt.
Sit in on a potential class or instructor one semester ahead.  This will help you in your choice of classes for the following semester.
Make an appointment with your undergraduate dean or advisor.  Ask for recommendations of courses and instructors.


The suggestion made in a comment by @lemon is good too.

I like your attitude.  Everybody has their own rate of development.  Late bloomers are welcome in academia too.

Do make sure you are solid on your foundational math skills.