There is no website or dealer that currently has an AR for sale, even in the secondary market, an AR is pretty rare, and when they do rarely get listed, they sell in about 2 seconds.
If you really want an AR, there are 2 ways to go about it.
First, keep a VERY close eye on the for sale forums, here on BF and elsewhere, if you see one, email the guy immediately.
Next, you can pre-order one from a Strider dealer, from what i understand, Strider is poised to release some AR's relatively soon. I know there is a tactical AR coming soon, which must be preordered, but im pretty sure i also heard Mick say that there were regular AR's soon to be in production, though i may be wrong about that. Either way, i believe that to get any AR, you need to preorder one and wait.
Those are really your only options, and unfortunately, i dont think you'll be spending your $400 today.
I still say the SnG is the better designed knife, much as i love the AR, but to each his own. Know one thing though, the AR is a GIGANTIC knife, its not the most practical knife for EDC, the SnG makes for a much better EDC.