Classerich,
I think I have a good idea about your situation.
Since the introduction of the SACD-M transport assemblies in the SA-7 and SA-11S2 players, Marantz Service Centers would only replace the whole SACD-M assembly, not just the laser. And since most all laser failures occurred past the warranty period, Marantz was under no real obligation to the customer. So the Service Centers told customers, and repair shops, that the needed part was not available. I have read a few instances of that happening on various forums.
With your SA-10 the Service Center seems to have done the same thing and told you that the part was unavailable. Yet, the SA-10 is still a production model, and Marantz supplies the SACD-M assembly to companies like DCS and Playback Designs. What Marantz likely does not have is a number of extra SACD-M assemblies for repair/replacement.
But all that is needed is just the laser mecha replacement in the assembly. And to that end, Marantz included instructions in the SA-10 Service Manual for mecha replacement. Why an authorized Service Center would refuse to do this is anybody's guess, as repairing units is the whole purpose of a Service Center.
In your case, your player was under warranty so Marantz had to do something, as that is what a warranty is all about.
I have a thread on a few forums asking is anyone has had a laser failure with a SA-10, Ruby, or SA11S3 player. There have been a number of views, but no posts. So I'm thinking you might be about the only one so far. Lucky for you that you were under warranty.
I would also suspect that your old player got repaired and made available for sale from an authorized seller like Accessories4Less. They would sell the unit as a Factory Refurbished unit for a substantial discount from the new price.