The government rationed food during World War II and gasoline in the 1970s. Now, it's imposing quotas on another precious commodity: 2008 dollar coins known as silver eagles.

The coins, each containing about an ounce of silver, have become so popular among investors seeking alternatives to stocks and real estate that the U.S. Mint can't make them fast enough. In March, the mint stopped taking orders for the bullion coins. Late last month, it began limiting how many coins its 13 authorized buyers world-wide are allowed to purchase.

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