If you are looking for a barrel maker that is going to have a web page where they actually say "yeah, we love to make one-off barrels for guns out of production for 15 years" then please do share all that you find.
Bar-Sto? Sure as hell actually, definitely, most certainly COULD do exactly what you ask and considering Bar-Sto's history with S&W 3rd Gen pistols, I don't think there exists a better answer for the task.
I think it would be funny to hear the price quote, especially if you opened the conversation first with "money is no object!"
My guess at their answer: 3,000 or maybe 5,000 unit minimum order.
This will be a tremendous benefit to you, as you will have a few back-up barrels, since money is no object.