I will be including some heroes that people main here in VCO that i'm aware of.
Mccree - Lockdown (Secondary)
Pharah - Stormpaw (Secondary)
Soldier: 76 - Lockdown (Secondary)
Tracer - MerryJade (Secondary)
Bastion - Dicerson (Main)
Hanzo - Outshadow (Secondary) - Stormpaw (Secondary)
Junkrat - Phantazem (Main)
Torbjorn - Phantazem (Ex-Main, Secondary)
Widowmaker - MerryJade (Secondary)
D.va - Lockdown (Main) - HastuneMiki (Main)
Reinhardt - AlbiePC (Ex-Main, Secondary)
Roadhog - Dragoncrazy (Main)
Winston - Dragoncrazy (Secondary)
Ana - Stormpaw (Main) - Lockdown (Secondary)
Lucio - Phantazem (Secondary)
Mercy - Outshadow (Main) - MerryJade (Main)
Zenyatta - AlbiePC (Main)
Now, Keep in mind. I will of course add your main once i'm informed of it. But, if your lvl 6 and say you main Widowmaker then i'm not going to add you. You have to have experiance playing with them. Not asking you to be Grandmaster with them. Just understand their way of playstyle and their role in a game and map.
Another reason why i'm making this. If you new to Overwatch and want to learn to play. Here's a list of players you can ask info from and play with. However, if your wanting to learn to main or play some-else and want to be better with them, you can ask someone on this list that mains or plays the hero you want to main or play.