I guess I misunderstood you, I thought you had removed the self-signed certificate and could not longer access the web interface.
The only way to get that CSR back would be to restore from a backup. See thsi document for more details:
Title: 'Error: "No stored certificate request matches this certificate" when importing a signed certificate into Symantec Mail Security 8200 or 8300 series Appliance'
Document ID: 2008031211054354
> Web URL:
http://service1.symantec.com/SUPPORT/ent-gate.nsf/docid/2008031211054354?Open&seg=ent