The criteria for being listed as a spice source on this page are a bit complicated. Of the spices commonly used in medieval European cooking, there are seven that are not usually found in local US grocery stores. If a spice merchant carries at least four of these seven spices then they will be added to the list.
The seven "Must Have" spices are:
ceylon cinnamon (Cinnamomum zeylanicum)
cubebs (Piper cubeba)
galingale (Alpinia officinarum)
grains of paradise (Aframomum melegueta)
hyssop (Hyssopus officinalis)
saffron (Crocus sativus)
saunders / red sandalwood (Pterocarpus santalinus)
Also known as: Wheat starch
(no sources known)
I have found wheat starch in stores that carry specialty foods from Asia. It is very similar to corn starch.