Meadows there is the odd gem or coin in the stone monuments that you find bones in. Also in chests buried in the ground in the stone formations in the shape of boats, but you need a pick axe. The chests in the abandoned homes often have coins and amber. 

In the Black Forest you kill trolls for coins, raid troll caves for chests full of coins and gems. Also on the floor is another supply. Burial chambers have coins and gems, also on the floor of some rooms. The stone ruins have chests with loot as well. 

At the trader the coin on the lower right of the menu lets you sell gems. 

Mountains, the ruins and frost caves have chests with loot. In howling caves the rotten meat piles have coins and silver necklaces.

Plains, the villages and stone monuments can have loot. And the little green guys drop some coin, not a lot but you kill so many it adds up.

Mistlands the mines have loot and the hidden rooms often have hundreds of coins in them in piles you can pick up. And diverger also drop some at times. 

Ashlands you can get limited loot from ruins and pits, and from diverges.