That's not the way it works. When it leaves the grower's hands, he doesn't know where it will wind up. And once a dealer is apprehended, there generally isn't any reasonable way to determine where his illicit drugs originated, or what paths the drugs followed getting there.
The original issue was growing pot on one person's property and the pot never left the property. Obvious that the two or three plants were for personal consumption. Do you claim that that falls under the interstate commerce clause?
Steve Kubby.