There is a "Randy" here on the forum that services
Hamilton equipment (validators). His forum name is simply "Randy", just click on "Members List" above and search thru the "R's"; click on his name to send a message.
You might also check with Suncoast
Changers - Scott Johnson. Again, they do validator work, don't know about controller repair.
Which controller are you looking to get repaired? Single line, double line, ACW II, ACW 4 etc? The older "double line" controllers are out there used; a new "Goldline" or some such probably ain't gonna be found.