Welcome to the Forum. I think Stick has pegged it for pre electricity moldings. The are most likely to have been hand made using a plane. Ordering a custom made, large bit for either a router or shaper is going to be expensive for your customer, since they have to pay for everything. Making a plane is going to be expensive as well, but you are not trying to replace long lengths of molding, so hand planing is likely to be a good option.
Finding old planes that match old parts like that seems a near hopeless approach to exact matching existing, antique parts. It seems to me that the leads in Stick's links to plane making instructors might be a good way to find someone you could work with to make planes that work.
I'd also suggest you recommend to all customers who choose to have exact match materials buy lots of spare material so they have spares in reserve for when other windows deteriorate or fail.
For plane making, I found a good source of oversized material for the body are turning blanks for a wood lathe. Some really nice, seasoned stock out there.
I am a very marketing oriented guy, and I can see you making videos and planting stories with lots of pictures in antique oriented publications and websites about how you do each and every job. Some clients might like that, and certainly local and regional magazines and even local papers would love to print such a spread. That would get the word out fast among the right people, and I'd make sure you clipped and sent a copy of each article and a letter and emails to antique dealers and other restoration oriented craftsmen, and to museum directors so they got to know you. I bet that would really produce access to some high paying restoration work. And specialty bit makers would soon direct people to you as well. You might also grow to love doing this kind of work. Or, you could team up with someone who has learned to make custom planes. Lots of possibilities here.
In any geographic area, I bet many of the parts you're trying to duplicate were made in the same local or regional shop. So if your customer invests in a plane or bit, you might be able to use it on more than one job. A piece of the old molding will give you a profile you could cut into a new plane or have cut into a new bit.
Either way, authentic parts are not going to be cheap and most of your customers should have a choice.
1. pay for a new commercially made bit.
2. pay for a custom made plane and hand work.
3. settle for a workable replacement using closest match material you can find and replacing all parts on all windows so they all match.
Whichever choice they make it is going to be expensive, but that's the way it is with authentic restoration, isn't it?
Personally, I'd really look into making custom planes. Once you get good at it, I bet there are museums and networks of customers who insist on authenticity, and that word will spread about you as the go-to specialist, if it hasn't already.
Last edited by DesertRatTom; 04-06-2016 at 06:34 AM.
Reason: Additional thoughts.