The Mauser M03 is a rifle that is still being produced alone mit-habengut-und-alles.(everything) Any good gunsmith ought to be able to make a spare barrel for the Mauser M03 from a raw rifled tube.
I think I had considered that previously and people on NE itself advised it would be difficult or impossible?
At the prioce M03 barrels sell for, a custom one shouldn't even be much more expensive done outside the factory.