Some of these pistols were converted to .380 ACP.
If 9mm Browning ammo were not available a chamber insert ring might work. A similar ring is sometimes used to convert .32/7.65 French pistols to .32 ACP.
The ring insert for the French pistol can be cut from a .30 Carbine steel case.
The ring is cut from the case mouth, coated with thread lock and inserted, on first firing it locks firmly into the chamber.
A 9mm steel casing should work.