http://www.locktonrisk.com/nrains/excess.htm
Quick searching is not instructive as to pricing, but I guess some homeowners policies cover gun accidents, and such insurance is not particularly expensive.
I'll just mention ratios, that I'm a USAA customer who's father was in the military (eyesight kept me out, but they have a special category for us because we're better risks), that I don't have very many guns, have a monitored alarm, and no longer get the no claims discount (http://en.wikipedia.org/wiki/2011_Joplin_tornado).
All that said, I pay 4 times as much for the extra protection needed to cover loss of my guns as I do for the liability insurance that's an enumerated part of my renter's policy, and the single instance liability they're on the hook for is 35 times greater than a total loss of my listed guns and scopes.
(On the other hand, if you're as sensible as you say, I have three words for you: no claims discount.)