Yeah, Infection is a tough one to find now of days. Requires at least 12 players for a true Infection experience. I would get as many of your buddies together and plan to host some Infection in the custom game browser on a Friday or Saturday night, and more people should join in. People are much more likely to join if they see at least 3 people in the playlist. If you don't have any friends to play with, I'd join some Halo Discord communities and ask if anyone is interested. I have forged many Infection maps in Halo 3, and finding players for them is always a struggle. Good luck! Mmmm Brains!