Hi,
Thank you for posting in Symantec community.
I don't think it's possible to pull the Computer Serial Number info via SEPM reports.
Maximum what you can get is 'Client Inventory report' - Use this report to see the number and percentage of computers that fall into certain hardware and software categories. Available information includes the computers' operating system, total memory, free memory, total disk space, free disk space, and processor type. For example, from the Client Inventory report, you might see that 22% of your computers have less than 1 GB of free disk space.
About Computer Status reports and logs
http://www.symantec.com/docs/TECH95541
However I will try to check is there any way to pull this info.