To find a piece of 100 year old molding for a Sears and Roebuck home might be a tall order today. I know of a few methods to get you something that will work that I have done in the past. The simplest is if you don’t need a perfect match buy the closest they make today and maybe rip something taller down to the right height and call it a day. Sometimes on the back or side of the house this is something that is ok as it is not visible. Sometimes I have removed a good piece from an area you can,t see and use it in the front and then did the above.
Secondly you can see if you can make the shape using 2 or more common shapes.
Lastly and the best method is to find a mill shop near you and go in with a piece and ask them if they have mill blades to make you that shape. It is a fairly simple shape they would have no trouble making. Have them run you off a few lengths and save them for later.