The silver coins is an exclusive coin of Lineagedos as well as the Gold Coins. You can get them through world drop (all monsters can drop it), by lore quests, events, daily rewards, voting or by finding Silver Coin Chests.
The silver coin is untradable but can be sold just in NPC shops for 3000a each. Is not possible to get this coin by donation. You can use them to buy some products by visiting Bodahn or get a Gold Coin by collecting 100 Silver Coins. Remember that with the Gold Coin you can buy valuable items from Bodahn’s Bazaar.
In relation to Silver Coin Chests, they are randomly distributed throughout the map and contain 20 silver coins each. There are a total of 100 chests spread at once all over the world.