9mm Nagant specifications

I read a thread from 2016 that gave the specifications for this cartridge but it did not have any information about what the factory ammunition velocity was. I am looking at a Belgium Police Double Barrel Rolling Block in this caliber and would like to be able to ocassionally shoot it with safe pressure loads. Also, does anyone have a source for brass or loaded ammunition. Buffalo Arms lists it but they are out of stock.

All replies and information is appreciated.