From everything that I've see, getting into NCAA replay is challenging, but certainly not impossible. Your best bet is going to be to attend as many camps/academies where it is offered (such as Pure Officiating, etc.) to get exposure to the concepts and mechanics of replay, where you can be seen by conference coordinators. You must also be above exceptional in your rules knowledge.
Check out rule 11 podcasts, they have several interviews with replay officials which are super interesting and can also give you more information and context around replay.