The K3S was discontinued quite a while ago, just before the K4 hit the streets.
Did Elecraft say they did not have KIO3 boards to sell you, or that they could not service the radio? I see no reason they would need a board swap if they service it, they should be able to troubleshoot to component level.
If they really are not servicing K3s because of no longer producing full boards, I think many of us will be concerned. Please clarify.