Where can I find Mega burger bun in Oberarth?

Mega burger bun can also be found in these cities:

Altdorf Baar Buchrain Buochs Cham Ebikon Einsiedeln Emmen Goldau Horw Ibach SZ Ingenbohl Kriens Küssnacht Lucerne Richterswil Rotkreuz ZG Stans Steinhausen Unterägeri Urswil Wädenswil Zug

You can also find this in Oberarth:

Desserts Dessert Baking Mixes Cake Glaze Peanut Butter Ice Cream Rice Dishes Vegetable Juices Instant Iced Coffee Cheese Roll Canned Fish