He arrives at the tower every Friday at 4-5 am EST. He's always in a random spot but if you look on the forums that morning there should be many posts about his location and what he has for sale. He sold a primary exotic weapon on this past Friday so I'm guessing hell be selling a secondary like the icebreaker. I'm hoping for him to sell the gjallahorn for the second time because I missed out the first time but we'll see.