First AR need sights help.

[User 1234]

That's because they want to sell you what they have. They is nothing illegal about buy this complete lower...
https://www.brownells.com/rifle-par...receiver-w-bcmgunfighter-stock-prod83804.aspx
and sending to your FFL.
Then buy the upper of your choice and sending it to your front door.

This ^. I was not suggesting that you ask the FFL to separate a finished rifle. All you buy from the FFL is the lower receiver, ideally stripped. You are apparently getting more involved with firearms again. I think you'd be thrilled to see how much useful information is already present in the NWFA forums if you spent some time reading the existing threads.