I have looked for this information too and have been unable to find the CVE ID's in the database. I'm assuming they are in the xml column of the iv_attack table. This field seems to be a Java Byte object but I haven't looked to see if it's possible to get data out of it.
If you open one of you IPS Policies and then open an attack definition you will see under the Description tab a section called Reference that contains the NSP ID and CVE ID for the attack, I'm assuming that's what' s contained in the xml column.
There is a Manager API Reference Guide that you can request from McAfee support, but I'm not sure what you can access from the API.
Please post back if you find a solution to this issue.