Hii Diwyani!
If you are talking about class 12th admit cards for private candidates, the admit card is released with the admit card of the students of the school in which you have taken admissions for giving your board exams. So, the school register you with the respective board from their side....and your admit card is released along with the permanent students of the school. Hence, keep an eye and just be in touch with the school to get the admit card. Hope this helps.
Good luck!