These sounds are 99% based on the ones used in the official anime.
Apart from ripped and mastered audio from the anime, I've used echo layers of Crysis 1 and Crysis 2, as well as a widely available stock sound effects which also happens to appear in Bet On Soldier. This was necessary, because that particular sound doesn't appear in the anime without background noise or music distorting it too much to be of any use.
The skin used in the video is a rather old one, which can be found here: Black Lagoon Elites V4
Getting it to work was a bit fiddly, because it is 8 years old. Upon installation I chose The_Antiparate's animations, because they capture Revy's use of her cutlasses best. Accordingly, the sounds included are named to replace the sounds that come with this animation. The included script is required to use the firing sound variations as well.
After the installation it's required to navigate to models; weapons and delete all files named something like this: w_pist_elite_single
Obviously, you can still download these sound effects, rename them and use them in any way you see fit.