Would recommend that you at least get an initial consultation with a competent gun rights attorney.
The AG is likely going to tell you that office cannot give you legal advice.
The Tenant Association might be of some general help.
Because your landlord says it is so, doesn't make it true. He can claim anything, but that does not make it legal. IMO he doesn't have a leg to stand on, but you will need more ammo than my opinion will offer you.