Hello,
The documents required for verification during counselling varies, depending upon the counselling you are going for. In most of the document verification processes, admit card for boards which is your hall ticket, is required. However since you have genuinely lost the document, I suggest you email the official website of the board whose counselling you will be attending asking what to do.
Alternatively you can also email to your HSC Board authority asking them for a duplicate copy of the document. You can also contact your school they can help you in this matter.
All the best!