not sure but the Model 1900 Swiss Parabellum must have the same construction and this parts are available.

for a gallery load its maybe possible to shoot a .308 roundball only with a 209 Magnum shotgun primer. just drill a 7,65mm Parabellum case out for this primer.
this would be a cartridge that did not cicle the action but could bring a roundball on airgun velocity.

wait a minute ...

here it is
http://www.lugerman.com/Pages/MainPages/Parts.html

Lower Frame Parts: 33 A
Main Spring Flat 1900, 1902 and Carbine
$150
2 on stock