Any specification on genre? I have a large array of electronic music that I could find something in, but I probably couldn't come up with anything classical if I were to try. I'm going to search for something (probably without lyrics) regardless, and respond around lunch. Lunchtime edit: mostly bass-y/trap stuff I've come up with at the moment. Also no clue if you're using Spotify or Youtube or something else.
LSL - B L O O D B A T H
noax - Invasion
noax - The End
Arzon - Devilman
SLIGHT - Release
Troyboi - Flamez (The Alexander Lewis Remix is a trombone cover)
brothel. - vi (and possibly vii)
Vincent - Rukus Vincent - Achilles XVII (Vincent) - Anax Lyrics Walls - V2 That's what my preferences would likely be (especially if you're narrating over it) Actually, have a 70's Disco song as well: CJ & Co. - Devil's Gun (not really dark, but I thought it would be interesting to include)
Edit 2: Re-ordered, added more, and struckthrough tracks I personally wouldn't call 'dark' enough. They might still work, but I'll try to save you a bit of time by putting the better one's first.