I'm from mid-coast Maine and have an "old fashioned double buttercup". I was trying to contact suzyt14 to see if she had found out how to get more of them, or how to propagate them. I've not been able to find out much about them.

She only posted here one time in 2015 so it doesn't look like she is active on here. The thread where she asked her questions had some answers as to where the plants may be found. I don't know anything about them.
The thread "perennial double buttercup plants" in Ask a Question forum

Those look like Trollius to me, although it's a bit hard to see the leaf detail.