Where can I find Mega burger bun in Arch?

Mega burger bun can also be found in these cities:

Balsthal Biberist Biel Bienne Brugg Burgdorf Derendingen Gerlafingen Grenchen Hasle bei Burgdorf Ipsach Kirchberg Langendorf Lyss Moutier Münchenbuchsee Nidau Solothurn Tavannes Utzenstorf Zollikofen Zuchwil

You can also find this in Arch:

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