Here are some links you can try:

Online practice tests:

https://www.prep.youth4work.com/Medical/AIIMS-Test

https://www.tcyonline.com/tests/aiims-exam

http://www.toppersexam.com/MEDICAL-EXAMS/AIIMS_38.html

You can download and practice past AIIMS question papers (answers also given) in the link below:

https://admission.aglasem.com/aiims-mbbs-previous-year-question-papers/

Good Luck!