I suppose, you weren't given any details? Like whose intellectual property you violated, the property itself or any timestamp?
Where did you stream? Twitch, I guess?
There aren't any replacement files for this specific mod, but the sound files are easily replaced by hand.
All music files are stored in
user>mods>XComFiles>SOUND
The files are taken from a variety of sources: Vanilla X-Com itself, tracks made by modders for modders, movies, etc. but most of all: other video games.
It is impossible for me to know, which tracks you got in trouble for.
IMO, the most likely culprits are:
THING.ogg from the movie 'The Thing' by John Carpenter (occurs frequently in Zombie missions)
FRO_PSY.ogg, 'Frontier Psychiatrist' by The Avalanches (occurs only once in the Asylum mission) (watch the music video, you won't regret it)
You can take any other OGG file, rename it, and replace any suspect music file with it. MP3 files can easily be converted to OGG by many different programs or online services.
The mod portal (and by extension, this forum) contains several music collections, which were made for X-Com-related projects or for use with Open X-Com itself. These shouldn't give you any copyright strikes.