I would have to travel to central Missouri for a Mennonite store
There are quite a few here in Central NY.
Anyway, check your local grocery store in their natural foods section, if they have one, or maybe their bulk section, or a health food store.
We’re spoiled here. We have a grocery store chain named Wegman’s and it’s the absolute best grocery store in the world. They carry almost anything and their quality is fantastic and their prices, especially on basics, can’t be beat.
My daughter who lives in LA says that when she’s describing Wegmans to friends of hers who have never heard of it, it’s like Whole Foods only three times the quality and half the price.
Health food stores carry arrowroot. EnerG makes it as well as Red Mill. Hubby is allergic to corn so we use it, or tapioca starch or potato starch for thickening.