you might try some of those end of the world survivalist sites, i know they sell foods that dont rot and keep unrefrigerated for years. i bet with a little research you could make your own.
Craft stores in the baking aisles - like a Michael's or a Joann. They will also have meringue powder but that has extra ingredients. Try to find the straight egg white powder, they should have it, or specialty grocery stores, but those craft stores with the cake decorating stuff have surprising items sometimes.
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