If you're on Android, you can try the mobacoin offers for trying out their other games. You can get up to ~700-800 coins that way, before the flow dries up.
If there are other shady ways, like coin generators, it is illegal and we will not talk about those here. I think the mods will ban anyone who does. To me, it is the same as forging money. And forging money is basically robbing everyone else holding that currency (because it devalues that currency slightly - Economics 101).
Those mobacoin offers are all bullshit, I triend once with many games downloading and didn't get a single coin, and later I get a message where they apologise for a failed attempt to redeem code. And they want me to try again. How can I try again, if I already downloaded and registered it?