Hello Ashish,
In this case that you need to get a copy of Cisco OS you will need to contact customer service deparment and request them the installation media.
You can contact Customer Service through one of the following ways.
PHONE : 1-800-553-6387
Email : <>>cs-support@cisco.com> cs-support@cisco.com subject line put
in "Missing CD/DVD Request".
Customer service will need as much of the following information you can
provide.
1. Reason for Request
2. SO#
3. SAS/SASU (or any other Software Contract #)
HTH
Please rate this post if was helpful
Walter Solano