Generally in France, however it is a metal that rarely turns up. Your other alternative is to place some on your lot. hold ctrl shift and c to open the cheats window and type,
testingcheatsenabled true hit enter then hold ctrl shift and c again and type in buydebug hit enter, then go to buy mode and view by object and there will be a new catagory to choose from (last line, last box) in her you will find spawners for, fish, plants, gems, metals, bugs, also tomb objects and ambition objects (if you have the expansion packs) When you place a spawner on your lot be aware it will take a couple of days for it to start working.
Don't forget to hold ctrl shift and c and type testingcheatsenabled false to get rid of the testing cheats when your done.