You need to consult in person with an immigration attorney who would review the RFE to determine exactly they are asking for. If you have a FOIA response, whatever documents you need may be there. Good luck.
Best to hire an attorney to deal with this and properly respond to USICS within the time allotted.
A Form I-102 application could give you a duplicate of the I-94 card you obtained upon admission, but you don't have time for that, nor do you have a passport with an admission stamp to show USCIS.
Hire an attorney ASAP.
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
You should have filed an I-102 with your initial I-485. I would definitely consult with an experienced immigration attorney but probably your best bet would be to file the I-102 immediately and then, if the I-102 is not adjudicated within 80 days, respond to the RFE with a letter explaining that you have filed an I-102, a copy of the I-102 receipt notice plus the same CBP response that you have already submitted. Make sure that your response to the RFE gets to USCIS before the deadline.
If your I-485 is denied you can apply again, you are only going to have to pay the I-485 fees again.