Riot tell me how the hell i get level 6 mastery tokens

Alright ive been playing shaco for a month straight and hes really fun but i only got 1 s rank out of all the games i played. Thats one mastery token. Ive played a lot of games with shaco and ive played him in every postion, ive gotten most towers and most dragons and go about 11/2 every game rounding up. with a lot of assists around 10 or 15. But how the hell do i get another s rank. this is pissing me off becuase i cant get another s rank and i dont try to be as toxic as i was but its starting to piss me off and lose hope in the game. Please answer me back and explain this is on the boards a lot and i cant find a real answer watching Brofresco or anyone. Thanks...