Below is a link that includes a list of certified testers.

Your local water dept. may also be of help.

Here is a link that might be useful: Cert. testers

While on the Landscape Board the past several years, we were approached by the backflow testers group.

Apparently they can test, but I don't think they can repair or replace, unless they have landscape or plumber license.

It's an area where more overlap of service is needed, but probably hasn't been fixed yet.

Landscapers can install, but I don't think they can repair a backflow, but I'm not 100% certain.

Why don't you try calling Down to Earth Irrigation in Tigard. They specialize in irrigation work. Maybe give a day or two for a reply.

If your unit tests completely good, then the process is really streamlined.