Not entirely sure, but they should be treated like military posts, and bases. No firearms, even when not federally activated. Irvine No-Good armory has big signs on the entrance gate, that yells "NO FIREARMS BY UNAUTHORIZED PERSONAL", The same type of signs you see at BG army depot, Ft. Knox, and Ft. Campbell.
I'll google it for ya.
Not sure how helpful this is to ya, but, the No-Goods' equipment, supplies, weapons, and munitions are paid for, bought, and owned by the FedGov/FedMil. So, I'm sure if you look into it, the cost to build, maintain, and run NG armories and posts, are covered with federal funding... So, just as a safe bet, consider all NG posts, Armories, Depots, etc to be Federal and OFF LIMITS for firearms for us mere, lowly Civilians.
Plus, NG and Reserve units are governed by Federal law, have normalized ranks found with the Federal military, and Service-people, and veterans of NG units are treated and given the same benefits, and such that FedMil has/gets...
Three useful links?
http://www.law.cornell.edu/uscode/text/32/104
http://www.law.cornell.edu/uscode/text/10
http://boards.straightdope.com/sdmb/showthread.php?t=514473
