Hey mate, I used some of my homegrown Chinook flowers for my boutonniere in March. That was perfect timing because it was just around harvest, but in September you wont get any fresh flowers. I think I have some in the freezer still on the stem, which could suit your purpose, but they will probably look a little dry and sad by then.
Let me know if you are interested and i'll send you a pic. If you want them you can have them.
Dave