Popcorn will work, but it makes a pretty "gritty" cornmeal. Not sure what to tell you as far as varieties which would be available locally. Dried sweet corn (sweet corn which has gone far past the fresh eating stage and was allowed to dry on the cob) actually makes wonderful cornmeal. Otherwise, there are dent corns, flint corns, and flour corns. Each has different characteristics when ground. Almost any commercially available "field corn" (grain corn) is going to be GM varieties, unless someone has planted some heirloom types.

Summerthyme