Your CBSE Improvement Exam admit card may or may not be posted to you, It depends on your CBSE region. If you get a letter from CBSE about your new exam center then you will have to collect your admit card from there.
You will have to confirm from the respective exam center that weather they have collected the admit cards from the CBSE for you or not. Generally they collect the admit cards from CBSE by 15th February and allow students to collect admit cards from there by 25th February.
Kindly note that these dates can change and you should contact your exam center as soon as you get the letter from CBSE.
If you don’t get the admit card even 2-3 days before the exam then you can contact 3rd floor of CBSE office, Patparganj, Delhi. Otherwise name and phone no.s of all other CBSE offices in India are given here.