You can buy em online. Communion wafers. They’re not considered “hosts” or sacred until after they’re consecrated. But I don’t know if this would actually work or not. You’re not supposed to chew them, but let them dissolve. As such, I’d imagine when you add the melted marshmallow they would just sort of turn into a blob of sugary bread. They’re like if potato chips tasted of nothing, and had the same reaction to moisture as Styrofoam does to gasoline