Apparently my skills at googling exceed yours. That's always a good place to start looking for information.
At least Prairie Nursery offers it and it seems to be available.

Thank you db, we are order some plants - some for the museum and some for the guys! lol

I looked up Prairie Nursery and was happy to see they have two shipping periods:

Spring = Apr/May/June

Fall= Sep/Oct

A good quality mail order nursery will not ship plants during the heat of the summer.

I can't get enough of the Sweet Fern, I see it mostly in its native setting. Dry, rocky, sandy soils that are acidic. It can form large colonies, when you walk through it it reminds me of pine. Not sure I've ever seen it in a cultivated setting. It doesn't grow thick enough to compete with grassy weeds. In the native setting it thrives on disturbance such as fire.

Reeseville Ridge Nursery in Wisconsin sells them as seedlings, about 2'. I haven't succeeded in cultivating sweet fern yet. I hear they are difficult. I had the sand. Maybe I should have added more acid. I will say the one time that I ordered plants from Prairie nursery they were all extremely root bound. I'll continue to with my rants till they have Dicentra exemia back in stock. Rootbound or not, I'll take them.

Jay, here is an article I found while searching for the plant - might be of interest if you still want to try to propagate them yourself.

https://www.amerinursery.com/growing/propagating-sweet-fern/