There are EXACTLY ZERO registered, transferable Glock 18s in existence. That is none, nada, never have been. It is a firearms myth. Anybody who claims to have seen one, seen one for sale, heard of somebody with one, etc. Is either lying or passing along a BS story someone told them. This is why there are no first hand accounts of them, it is always a "friend of a friend" or "some guy at the gunshots told me about it" type of story.
The Hughes Amendment to the McClure-Volkmer Act of 1986 banned machine guns manufactured after May 19, 1986 from being transferred or possessed by private citizens. It only effected imported machine guns by no longer allowing licensed dealers from keeping any machine guns imported after the cutoff date after they gave up their license. This is where the division between "Pre 86" and "Post 86" dealer samples comes from. In 1968, as part of the Gun Control Act of 1968, importation of machine guns was restricted. Machine guns imported after 1968 cannot be possessed by private citizens. The only exception is if a licensed dealer (SOT) acquires a machine gun imported between 1968 and 1986, he can keep the gun after he gives up his SOT. But if he gets rid of the gun he can only transfer it to an SOT or to a government agency. It cannot ever be transferred to another individual.
Since Glock was not making any firearms in 1968 (they were in business then, just not in the firearms business) it is impossible for there to be even a single transferrable Glock 18 in existence and since Glock did not import any Glock 18s untill after May 19, 1986 there are no "Pre 86" dealer sames either. The first Glock 17 pistols only reached the US in March of 1986.
Anybody claiming different should provide proof in the form of a copy of an approved ATF Form 4 listing a Glock 18 and without a restricted transfer notation stamped at the bottom.
Was an ATF liaison for a licensed machine gun manufacturer and importer. It was my job to know about these things.