Incidentally, corn poppies (Papaver rhoeas), cousin to breadseed poppies, appeared in war fields near WWI mass cemeteries in Belgium. The scene of endless red poppies emerging in that disturbed soil was so moving, it inspired poetry, and of wearing red poppies as a sign of remembrance.
I can’t advise you on the legality of growing seed poppies. However, many poppy laws factor in a gardener’s intent when growing them. If your reasons are beauty, seeds, and as a meditation to open your heart to greater understanding of other cultures—unless law enforcement has reason to doubt your integrity—there’s a good chance you can grow them legally.
Harvest poppy pods when they are fully colored but before the vents open if you don’t want any accidental seeding. Clip the stems well below the pods, collect multiple stems together with a rubber band, and set inside a paper bag to finish drying.