You can pursue diploma from any recognized university where they also offer NCC. Youcan enroll in any course where they offer NCC. But the condition is that theinstitution should offer NCC also. And because you are a C certificate cadet so the institution will have to give a seat to you on the basis of your B certificate without much selection procedure. If a cadet who has completed the second year and enrolls in some other institution then the institution is liable to give a seat to the cadet so that she/he can complete the course (even if it is from other battalion). But clearing the entrance of the institution is completely in the hands of the cadet.