What are green 50% cards what I can not receive?

Probably these are the clash of zones 50% bonus score tickets. You can get these as rewards during clash of zones events at certain points. The best way to get them is to make sure you join a strong alliance that can rean enough points each day to get the 3 alliance reward boxes.

You can also earn them yourself. Check in the clash of zones event for these.

If it is not these tickets please let us know more details on what it is you are seeing.