Where to get dukka coins?

mine just appeared in my inventory all of a sudden i don't know how

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Dukka Coins (Dukka) are the main currency of Dukka Town and Dukka Caves. When buying with Dukka Coins, shops only accept the exact coin for the item you buy. Dukka Coins may be obtained at the Slot Machine in Dukka Town, by Archeology in Simeria, Millionaires Lodge in Jenoa, and periodically in Account Upgrades or for event prizes. You can use the Dukka Exchange without any limitations, except for depositing 10 or bigger Dukka Coins, you'll be charged 10%. It will take away 1 dukka per each 10 you deposit.

http://maradanchronicles.wikia.com/wiki/Currency#DUKKA_COINS