There is nothing about it on the General Info Page for the site:
You may be thinking of the following: Sec. 512 of P.L. 111-24, an amendment to the Credit Card Accountability, Responsibility, and Disclosure Act of 2009, covers National Parks and National Wildlife Refuges. I do not see where National Cemeteries are covered by that law and it appears these are under the control of the VA and not the NPS.
There are a few other links with similar info (Google "national cemeteries firearms"):