I never did find a way to get Eterna to supply a crystal to their own authorized service provider.
But he was able to source a case and crystal from a customer who balked at the repair cost of a similar model and sold the carcass to the shop.
And so now my Madison is back in hand, with a mint case and crystal and a fresh movement service.
As originally bought:
And 23 hours later:
And then nearly 14 months after that:

It was a far longer wait that it should have been,and my bargain ended up costing well above market, but I still have that new watch feeling.
—Rick