dried corn kernels
Fully mature, hard-dried maize kernels, not sweetcorn; the starting point for nixtamal, masa and pozole.
Dried maize kernels, usually white, yellow or blue field corn, or the large-kerneled cacahuazintle for pozole, are rarely found in supermarkets and more often in Latin American shops, mills, well-stocked health food stores or by mail order. They have to be soaked and cooked for a long time or nixtamalized with lime; canned or frozen sweetcorn is a different thing and won't work.
Substitute:
For pozole, ready-cooked canned or jarred hominy is a good stand-in, just a little softer and less corny. For tortillas and tamales use masa harina, the already nixtamalized corn flour, instead; ordinary cornmeal or polenta won't come together into a dough without nixtamalization.