Have you considered what is involved in making the device you are talking about having made? You want whoever makes it to make only one since there probably isn't much market for such a device. Off the shelf parts (Including lenses folks) are cheap because they are made in quantity which reduces the cost to the manufacturer by spreading the set up costs over many parts. When you want something custom made, all the set up costs get passed onto the customer. Have you ever seen an inexpensive hand made one off car?
I can make the adapter you need. Please email me if the previous paragraph made sense and you still need your adapter.
I need to have a lensboard oddity manufactured - I need a Phillips/Horseman/Sinar extension lensboard made (three inches of extension)which is then an adaptor board to fit Linhof Technika boards.... I spoke to SKGrimes about it, but $550 sounded too rich for my blood (sounded way over the top to be honest - I am still not sure how they manage to charge 60% more for a simple shutter CLA than most technicians do...). I would think that a competant woodworker should be able to manufacture such a thing without too many problems - anyone have any pointers to such a person?
Sinar did make a 3" extension board with a Copal 3 opening. This was a standard product available from the distributor. Sinar dealers can check to see if it is still available. Cost was less than $300 from what I remember.