Where can I find Baking soda in Oberarth?

Baking soda 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:

Pudding Decorative Sugar Three-Grain Bread Cereals Delicatessen Sausage Spice Pastes Mashed Potatoes Raisin Roll Canned Sausage