Much less risky than growing your own, and with guaranteed results, is to contract with a nearby large garden center or florist or grower.

Consider that sunflowers may likely be well past their prime by November.

I live in San Diego county (so maybe a bit warmer) and I've been growing rounds of sunflowers from spring and some are still coming! I have a round that should bloom around Christmas! Here's one from a few days ago, a Moulin Rouge variety. The others are flowers blooming in November, yellow sunflowers, garden roses and dahlias. what about calendula and long stemmed pansies? Check out on Jan 2, floret flowers
https://www.floretflowers.com/ she'll have an amazing range of flower seeds available! What a nice idea from you to grow flowers for your friend's wedding! My wedding was in October (13 years ago). My Mom and I did all of the flowers from a local farmers market. Burgundy dahlias, orange roses and yellow sunflowers, they were beautiful and we had some quality time together making our bouquets, and centerpieces! It is still special to me. Let us know what you decide on!

My unfortunate experience is that you may have the plants with blooms that are either non-existent or ratty-looking when you need them.