I think the roads you described are as good as it gets for the Eastern half of the nation.
The blue ridge mountains heading even into PA offer some excellent roads thate are not to crowded. I think so of the best ways to do this is to figure on sites you may want to visit and taking the back roads to them.
The Matt Farah method of finding good roads: "Find mountains on Google Maps, look for squiggles". I don't have mountains in Michigan so I look for roads that follow rivers.
I've been introduced to a few good roads via the Roads app. The app itself is not great as the navigation kind of sucks and it's just far too buggy, but with some effort you can extract the good routes and then put them in something like Rallista or Scenic that is way better.
There are probably many other ways to find "crowd-sourced" routes but Roads has been helpful for me. Also consider joining your local Porsche Club of America chapter, they'll do tours or rallys that are probably one of the best ways to learn great routes in your area. You don't need a Porsche to join.