For starters, and you are going to get a wide variety of information on this, but I would have stock cut with my own blades, assuming nothing is out there close enough to what you want.
Then, you can control the product you are milling. If you are painting, and I would assume you would be, you can get stock that is very stable and less apt to warp or shrink.....around here, that would be poplar. Very fine grained.
There are "man made fiberglass" moldings that are really good. They are worth your time investigating. They take paint great and also are totally stable.
If I were your, I would go around looking at restored homes. There "has" to be some in your area. And, the owner's "have" to be extremely proud of their work. Take a photo of your home, and a history of it. This is like talking about your kids. No one will want to turn you away.
Just a thought or two.
I will add if I come up with some other stuff. Of course, you could hire a professional if you have the budget. Considering your project, this is not entirely out of line. A professional interior designer is up on this stuff. And, they have a line on "appointments" to complete the job. If you are having your house restored by others, he is a good guy to be the manager. If you are doing it yourself, he is a good guy to help you out too.
Depends on your specific situation and your "back to the past" thing.
Remember, you will want to hide all those modern gizzies like outlets, duct work and supply vents, lighting, et al.