There are a number of ways to get Gems:
● From specific wonders of the world (like the Gem Mine and Gem Gargoyle). These can only be acquired by collecting the card pieces for them.
● Premium Account Perks (you can find out more about the premium account here!
● By certain winning contests in the forums (these don't take place often, but be sure to keep an eye out for them!)
● Occasionally, Gems are offered as an option for a bonus gift when buying Gold Bars.