Dear Aspirant

The migration Certificates are given off by the institution you completed your XII from. The process of acquiring the same also varies . Please contact your institution and inquire about the same.

DOCUMENTS REQUIRED FOR AIIMS COUNSELLING
The prospectus of All India Institute of Medical Sciences (AIIMS) states that those called for counseling have to report with the following documents/ certificates in original:
Admit Card
Call Letter issued by AIIMS, New Delhi
Proof of Date of Birth Certificate/ Mark sheet from the Board from which the candidate passed the 10+2 or equivalent Examination. 
Migration certificate from the University/Board last attended
Category certificate (if applicable) 
Current passport size photograph (front pose) 6 copies. 
One set of self attested copies of all the certificates