Expert repair of Vintage Tube Amplifiers

I own 14 vintage tube amplifiers. They are all working.
I want to upgrade a circuit in all of these tube amplifiers but I don’t have the technical knowledge to do the work myself. 
I live in NE Pennsylvania. Finding a repair/creative modifier technician I can work with in my area has been a source of frustration for years.
I would probably have more success finding a talented person who builds their own tube amps but for them Audio is a hobby, not a business. 
Does anyone have a suggestion that could help me find a path that could lead me toward a fruitful direction? 
My unique business plan, plus the ideas and products I have already developed, could lead to an exciting opportunity. For the individual or business whose experience and knowledge can fulfill this critical need,
there is a strong possibility that a successful outcome can be achieved.
I welcome any and all feedback as well as criticism pertaining to what I am doing incorrectly.

What is it that you want to upgrade? Swapping out diodes and caps can net you big improvements with little more than a soldering iron. Anything beyond that and you are no longer talking "expert repair" you are into circuit design, which is a whole different thing. So what exactly is it you’re looking to do?