One of my favorite bandom m/m/m fics is It may not always be so which is a sequel to Sing terribly afar.
And there's also Fair Market Value (Ryan/Brendon/Spencer) and Wednesday Night Boys (Ryan/Brendon/Jon) but I think you might have already read these two?

I know that I've ready more bandom m/m/m fics, I distinctly remember a werewolf!au with Frank/Gerard/Mikey and another werewolf!au with brendon/ryan/jon but my fic bookmarking system leaves a lot to be desired. :(

There's also a few other m/m/m fics I know but they're in the Harry Potter fandom, if you're okay with that let me know!  ♥

Bandom_meme! It's on my to-do list to be more active in the comm this year!