Couldn't find the link to download the file.
Hello Pavan Kumar Nallam,
Per our release notes documentation the custom assertion instillation files are part of the CA API Gateway CustomAssertions-9.2.00 archive for 9.2, file name GEN12152731E.zip. This file can be downloaded from our support site. Once logged into our support site go to you product downloads, select the 9.2 install and download GEN12152731E.zip from the available downloads.
Release notes: Release Notes 9.2 - CA API Gateway - 9.2 - CA Technologies Documentation
Normally, you can get it from support.ca.com, but 8.2 is too old and not in the download list anymore.
You may open a support ticket to ask the one for gateway 8.2
But I would suggest to upgrade to latest gateway version, and download the component you want on support.ca.com