There Is No Hack For Clash Of Clan Gems, But You Can Install iMods If You Are Jailbroken.. That Has Some Mod Options
There is no hack for Clash of Clan just some option as Yesca sais ! I thing you CAN find some hack with Flex 2
Unfortunately you need Jailbreak on Iphone to mod CoC. On android all you need is a modded APK. I cant link you anything since that kind of info is GOLD members only. Goodluck though.
If only there was something proper for android but the amount of server checks that are used is unreal even if you do find something that 'works', you'll get a 'client and server are out of sync' error and will be forced to reload the game