The other museums may be publicly funded, but privately managed, and set their own policies. So not against the law to carry, but would be subject to tresspass if refused to leave.
I recall a sign near the IMAX, (a real IMAX by the way, not a FAKEMAX) that had a gun with a slash thru it , and "NO WEAPONS" in bold print. So I would assume the ISM is out on CC.