UM_AaaBattery: That would not be the right statement, It is in fact possible to "unlock" Kolos through mission. This option would take a very long time and effort but it could be done.
DvSMerkz: You will be better off just buying packs or buying him off the market. You might have some cards you can put together to trade for Kolos too. Like I just said, you would have to do a lot of missions to get Kolos and I don't think it would be worth your time and effort.