Why do you believe that you need a CTO? Your post, while short, seems like what you really need is a programmer or two.

Presumably, someone wrote the program which you have been contracted to provide to customers? Why can't you go to the original party who wrote the program? Is "contracted" the correct word in your case? That would mean that you have already entered into a written contract to provide something to customers.

Or, are you saying that you entered into a contract to purchase a program, you showed the program to some people, they want some changes, and you need someone to change the program?