I know you're in the States and this won't apply to you, but I thought I'd post this incase another Canadian searches the postings:
I just found out that Visual Arts Ontario
offers studio and art transportation insurance. And here I've been paying The Co-Operators much more premium for much less coverage! Guess who's going to try to weasel out of her existing policy and take advantage of another one
My suggestion is to exhaustively
contact all of the artists' societies/groups/etc to which you could have membership, and ask whether they offer the type of insurance you want. VAO was (I kid you not) the only
group I didn't contact... and that's only because I gave up after a while and assumed that no Canadian group to which I have access had an insurance policy for their members.