I've got avatar-sized models of all currently circulating U.S. coins for sale over at the sim Siringo (coordinates: 178, 175, 39). You get pennies, dimes, half dollars, nickels, quarters, presidential dollars, Sacagawea dollars, Susan B. Anthony dollars, and Eisenhower dollars from one box. The other contains about 28 state quarters.
You can find a lot more coins, and buy them individually, through SLExchange and OnRez. Together, the circulating ones cost L$175, and the 28 state quarters cost L$300. Also on those sites are Canadian toonies, Malaysian ten sen coins, Japanese five yen coins, many others from across the globe, and old U.S. coins dating back to the colonial times.
http://slurl.com/secondlife/Siringo/178/175/39/
http://www.slexchange.com/modules.php?name=Marketplace&MerchantID=153227
http://shop.onrez.com/Ash_Meersand