Hi, 

Trying to sort out character sheet to get Greatweapon Master. I'm not getting it as a feat, even went through google for idea how but nope. My barbarian can be a sniper or grappler lol just not weapon master. Any idea where I went wrong? Can anyone give me a list to follow to get what I'm trying to get?

Thanks.

Have you bought the source material where GWM is available?
Not all Features, races and sub-classes are available for free.

Or another option is to create this feature yourself so you can use it.

So basically you can use any feature, that you have written yourself.