This page has a few starting point suggestions for each of your topics (although I have lumped together several of them into the broader category Minerals & Mining).
About the articles from encyclopedias such as How Products Are Made and Encyclopedia of American/Global Industries: these can help illustrate the processes involved in the production of your commodities/products.
Immediately below are a couple of databases that most groups will want to use.
The sources below will be useful for most of the agricultural products.
The sources below will be useful for most if not all of the metals/minerals groups. This includes all the following:
Aluminum | Bauxite | Gold |
Helium | Platinum | Tungsten |
As a type of grain, you may search keyword 'corn' within the 'grains' category.
Fitch Solutions covers this sector well. See reports below.