I just spoke with a very nice lady at Linder’s. Unfortunately it’s too late in the season for the seeds to germinate and take, plus the seeds may not be “ripe”. She told me what to look for in the seeds to know if they will be viable at all, but said they don’t transplant well so that may not be a good option either.
Short of finding one and transplanting it though, I fear I have no other options - it can’t be grafted since it was totally broken off.
The link I provided had two dozen nurseries in teh twin cities area. You will need to search phone numbers on the web but one of them probably has a big sunflower you could dig up and replant.