this is a very different kind of course that has its eligibility different as per the corses.

if you are willing to get this degree under AIIMS, the registration must have been done in the month of march and the exam would be scheduled in June or July.

refer to the link

https://biotechtimes.org/2017/07/16/aiimsall-india-institute-medical-sciences-msc-entrance-exam/

for info about the exam.

you can either buy AIIMS Explorer or such preparation books from amazon or flipkart for 300 INR 

also i'm here by mentioning the link from where you can download the question paper pdf

https://www.freshersnow.com/aiims-msc-previous-question-papers/

https://www.google.co.in/search?rlz=1C1DVJR_enIN791IN791&q=aiims%20msc%20entrance%20exam%20question%20paper&ved=0ahUKEwjjz-e9rbnbAhXDRY8KHS4IDDAQsKwBCDwoADAC&biw=1280&bih=615

all the best