Call your local fire department and see who they use. Kidding aside, the circuit is quite simple and most competent techs can service the amps. Have you tried contacting KR Audio USA https://www.kraudiousa.com/index.php
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You want to work with Renaissance Audio in Ann Arbor, Michigan. They are the Authorized Service center for KR in US and Canada. Bradley Smith is who I talk to and he is who introduced me to Eunice Kron who is the actual owner of KR. Follow the "Contact Us" link at this website.
If you run into any issues PM me and I will send a note to Bradley introducing you. I sell KR Tubes and have a relationship with KR directly as well.
You will get no response from the KRAudiousa.com website as it has no affiliation to KR and hasn't been updated in years.