Or a black market knock off.
AR type rifles aren't exactly hard to find and get. Insurgents don't tend to use them, because they're harder to keep clean, and use.
[Edit]: There are reports that the afghan taliban equipped their better trained, anti-daesh cells with AR rifles, along with body armor and helmets, bought from corrupt ANA soldiers and officials. Just an interesting note.
Or support neither, because the lesser devil is still a devil.
The afghan taliban have never been Pakistan's allies, even if Pakistanis have deluded themselves into believe such a thing. Let us never forget that when they were in power, they threatened to invade Pakistan, if Pakistan tried to enforce the international border.