You have not revelaed either you did under CBSE or Stateboard, however in Tamil Nadu Govt, you can get Duplicate Marksheet.. Please see the procedure.. but it will take some time, the same should be the procedure followed every where,
Please see the process in case of Tamil Nadu.. check with your School HM,
Remedies on Loss of Certificate
Candidates can get the Duplicate Certificate or Certified Copy of Mark List in case
of loss of certificate or destroyed by flood or fire. Certified Copy of Mark List is only
valid for short time duration whereas Duplicate Certificate is valid for ever.
Immediately on loss of original certificate the candidate must lodge a complaint in
the nearest Police Station. If the certificate is not traceable, the candidate should
obtain a non-traceable certificate from the Police.
Based on the above Non-traceable certificate, loss certificate from the Tahsildar
concerned may be obtained.
If the certificate is totally destroyed by flood or fire, a certificate to the effect has to
be obtained from the Tahsildar concerned.
If the certificate is partially damaged and cannot be used, the same should be
enclosed with the application for duplicate. In this case there is no need to get nontraceable
certificate from Police of from Tahsildar.
For more details please see the link : http://www.tn.gov.in/rti/proactive/sedu/handbook_dge.pdf