I wouldn't try to transplant them if they are already blooming. You might be surprised how quickly cosmos will produce seed. I bet you could have seeds in two weeks. You'll need to protect the flowers once they have faded, to keep birds from eating the seeds and knocking them onto the ground. I've used old nylons or tulle bags from the wedding department at craft stores. Tie them around the faded flowers and let them catch the seeds as they dry. Good luck. If you don't manage to save any seed, I've got lots that I've save in the past year or two that I'd be happy to donate.

Martha

Thank You!