I get the Peru giant kernel corn locally where it is sold for food .

For giant pumpkins the best place is Howard Dill. He sell all kinds of premium seed with the parentage listed for each one.

Here is a link that might be useful: Howard Dill Atlantic Giants

"Weeks seeds " and "Thompson & Morgan" have a large selections.

anyone know when weeks is going to open back up from the fire?

The biggest selection of giant varieties is P&P seed company. http://www.pandpseed.com/

If you are looking for seed sources, the best thing to do is do a google search for what you are looking for. For example, if you are looking for giant sunflowers then do a google search (and google image search as well) on "giant sunflower" "tall sunflower" "tallest sunflower" "biggest sunflower"... you get the picture. You find information such as online news articles about a sunflower at a local fair. You then use that information to track down the person. If they give the person's name and hometown you can use a people finder, like zabasearch.com to find the persons address and telephone. You call them and politely ask for some seeds. This is generally the best way to giant material. Google searches are the best way to research giant varieties. One piece of information always leads you to another piece.