I am going to keep looking but it is actually referenced here on this site but no saying where in the law.
NYS Gun Laws | NY Firearms - New York Firearm & Gun Ownership, Laws, Politics, Weapons | NY Firearms
Edit: This might be it.
265.02 Criminal possession of a weapon in the third degree.
A person is guilty of criminal possession of a weapon in the third
degree when:
(1) He commits the crime of criminal possession of a weapon in the
fourth degree as defined in subdivision one, two, three or five of
section 265.01, and has been previously convicted of any crime; or
(2) He possesses any explosive or incendiary bomb, bombshell, firearm
silencer, machine-gun or any other firearm or weapon simulating a
machine-gun and which is adaptable for such use; or
(3) He knowingly has in his possession a machine-gun, firearm, rifle
or shotgun which has been defaced for the purpose of concealment or
prevention of the detection of a crime or misrepresenting the identity
of such machine-gun, firearm, rifle or shotgun; or
(4) Such person possesses any loaded firearm. Such possession shall
not, except as provided in subdivision one or seven, constitute a
violation of this section if such possession takes place in such
person`s home or place of business; or
(5) (i) Such person possesses twenty or more firearms; or (ii) such
person possesses a firearm and has been previously convicted of a felony
or a class A misdemeanor defined in this chapter within the five years
immediately preceding the commission of the offense and such possession
did not take place in the person`s home or place of business; or
(6) Such person knowingly possesses any disguised gun; or
(7) Such person possesses an assault weapon; or
(8) Such person possesses a large capacity ammunition feeding device.
Criminal possession of a weapon in the third degree is a class D
felony.
I copied the above from a different site since the official NYS webpage with the laws is down. I double checked the above from a different site and it didnt say 20 so maybe the law has changed and we are thinking of the old law?