HI Aspirant, 

You should clear entrance exams for getting Admissions. As you would know , MS after BAMS is not like ordinary MS after MBBS , here MS involves surgery via ayurvedic techniques. There are many entrance exams which are conducted for MS . These exams include - JPGET, JPGEE , PGET,UPGMEE, BHU PG entrance test for MS (Ayurveda) . Also there are various private institutions which conduct their own entrance exams for MS in Ayurveda. 

Good Luck!