Welcome back! Finding commercial sources of native plants can be rough here in IA, I know there are a couple that people have mentioned, but for the life of me I just can't recall them. However, a good online source is Prairie Moon Nursery at prairiemoon.com. I've had good luck with them, although I'm not sure what they have for shade loving native plants. You might try looking for Jack in the Pulpit, Virginia Bluebells, blue phlox (sometimes also called Sweet William, but not the type of Sweet William you often find in garden centers)...all of these are herbaceous perennials which are native to Iowa and thrive in shade. There are actually a lot of native woodland plants which flower, but I'm not sure how many are commercially available. An excellent reference book is "Wildflowers of Iowa Woodlands" by Runkel. It was printed by the ISU Press, however it is no longer in print and you'd have to find a used copy. Try abebooks.com, that's where I got mine. Hope this helps somewhat!

The the Ion Exchange in Harper's Ferry in northeast Iowa. They specialize in native plants and have a large selection. They have a website but I don't have that address. They're very knowledgeable and they will be able to give you lots of suggestions.

Cricket

the only one i can think of right now are dutchman britches.