Yeah I know. They have to be made pre-1986 and they're insanely expensive. Finding a fully automatic AR is basically impossible though. Unlike other guns like the MAC-10 which were sold on the civilian market as fully automatics before the ban, AR-15s were never sold to the civilian market in select-fire configuration. All civilian market AR-15s were semi-automatic only and by the time the patent expired on it, there were very few other companies making any AR-platform rifles before the ban in 1986, and those that did (like Bushmaster) only made semi-automatic.

There are some very rare pre-1986 M-16 rifles that made their way down to the open market, but you're looking at $40,000 up to $70,000 for them. There were all of 6 M-16s available on gunsinternational, and the cheapest one was a pre-ban lower receiver and buttstock for $38,000. The cheapest full rifle was $43,000.