Yes, every month there is 5 different games you will earn Zsilver by playing. If you look in Cortex, under 'popular games to earn Zsilver', these are the games that will get it to ya this month.
As said above, There are certain games per month. You can vote for next months game here. (Top 2 voted get put in, 3 others random from Razer) You can view this months list here. They also do rotations every weekend it seems as of so far that either have double the ZSilver cap, Double the amount you make per minute (3 to 6), and sometimes rarely, They do both of it.
If you want you can make some suggestions? Razer reads these boards all the time from what I've observed. They could see your post and add it to the game list possibly. Just because Razer isn't vocal, doesn't mean they aren't watching.