I'd like to buy a few Hammernes to fix up some weapons which are getting close to breaking. But where can I buy them? Do any of the Wireless Bonus Teams sell them?
The only way it's obtainable is through Anna or random streetpass teams. Anna will occasionally sell "rare" items. For example, depending on the location, she will randomly choose between 10 items and sell 3 of them. One of the items she can pick is "Rare" (30% on most maps). If she picks "Rare" she will randomly pick another item from this list: Hammerne, Seraph Robe, Energy Drop, Spirit Dust, Secret Book, Speedwing, Goddess Icon, Dracoshield, Talisman, Arms Scroll.
On later chapters and on spotpass chapters, anna will pick Rare 100% of the time giving a higher chance for Hammerne making the best spot for Rift Doors.
More info about that here: http://serenesforest.net/fe13/shop_merchant.html
Anna (via random appearance or summoned from a Rift Door) may sell Hamernes. Or a visiting StreetPass party may sell them; but the Hammerne is not available through any current Wireless Bonus Team.
However, I did discover these Wireless Bonus Teams selling some interesting goods: