What do you need? You're FIN-Fingerprint Identification Number? That's all you really need. It should be written on your I-94 or US Visa. You may also try to submit a FOIA to USICE.
I agree with my colleague. Your NSEERS number should start with FIN and followed by numbers. It is usually on the I-94 Arrival/Departure document (white card) or written on the U.S. Visa Page. If you cannot locate it, contact the local Immigration and Customs Enforcement (ICE) in your area.