Locating Water Lines & Installing Master Shut-off Valves

This last winter we had a several of our water lines break and had to shut down the water to all the homes in the park because we have no master shut-off valves for sections of the park.

How would we go about finding and installing shut-off valves? Have any of you done this before? Are there national water line detector companies that will help us find the lines? Should we hire someone to plan the best location for the shut-off valves and help us decide how many we need?

Need a little help from friends.