help finding a Roman Ogee / Window sash bit

I'd use a sash bit that gets you close, then replace all the trim on all the windows that are close together. If the shape is close, only you will notice it.

You could use several bits, and cut the basicshape with an angled blade in a table saw, then use a roundover on the tip, and a cove bit for the outward curve. But I would only do it that way if I were only replacing the sash in one window.

What is the longest single piece you need to make? this doesn't seem difficult to replicate using two router bits and a table saw.

Joe

Check the trim on display at HD or Lowes. Take a piece in with you and see if they have it, or something very close. Quarter inch by about 2/3rds inch is tiny., too small for the table saw. or router. Sorry I didn't catch the actual size of the piece before responding. You could replace this in every window in the house for $20 or so with something close, and it would all be uniform. Pre finish and experiment so the stain doesn't clash with the old wood.

Window sash making was big business back in the 1890s. Lots of specialty machines were made for the various joints. The muntin and sash bars were all made in one piece. The glass was put in with putty and glass brads. The components were made on a sticker (moulder). The cutter profiles were ground by hand. Good white pine was everywhere.
Grinding your own profile for a shaper cutter would be the easiest say to get exactly what you want with no compromises. I don't think HSS cutters for a hand router are available these days but if they were, you could try to grind your own profile in them. I've done a few over the years and found it tedious and exacting.

Do some research on how the window components were made back 120 years ago.

@rfsurfer I'm curious about what you wound up doing. Lots of suggestions and interesting posts, but what did you finally do?