Okay, I just got it without pickpocketing him, but it was still underhanded the way I did it.

I dropped an Ebony War Axe on the ground by him, then had my follower attack him. He grabbed the axe and unequipped the bow. I used the Voice of Emperor power to calm them down, and it was available for sale.

To guarantee seeing him, go into the Dwemer ruins just north of the outpost, and wait until after midnight. Save and exit to the dashboard. Restart the game from that save, exit the ruins and walk over to the outpost. He's there every time I do it that way.
I'm still curious if there's a more legitimate way of getting it though.
