Well, I tried looking for headsets myself but NONE of them match the tf2 style. I'd recommend looking up ear protectors on EBAY or at your local Thrift store. With the protectors you just have to worry about the shape and paint the rest whatever colors your need.
For the mic and headband You should find a cheap pair of headphones you don't mind gutting. I just the mic from an old Xbox headset, painted it whatever color I needed it to be, and glued it to the side after making a flat area for it to rest on.
And thanks for asking ! This was actually my first cosplay item I've ever made for my first cosplay ever