I blogged about the US Mint depleting their inventory of Gold Buffalo coins a couple days ago:

http://gregnguyen.blogspot.com/2010/09/us-mint-has-run-out-on-buffalo-gold.html

Last month, they had depleted their inventory of the more popular Gold Eagle coins.

http://www.bloomberg.com/apps/news?pid=newsarchive&sid=aKIgT9DddcYY

The Silver Gold Eagle coins have at times been sold out as well. This is not supposed to happen when an asset is in the throes of a long-running bull market. Higher prices should invite more production.

For instance, if wheat prices soar (like they have been due to drought in Russia), more farmers will allocate their acreage to production of wheat in order to increase profits, eventually bringing prices down to equilibrium. Gold was priced at $35 an ounce until President Nixon took us off the gold standard in 1971. It is now priced at approximately $1300. A much higher price should yield much higher production, as mining companies are motivated to produce higher quantities at inflated prices.

The problem is that an increase in supply has not accompanied gold's price increase, because there is no easy gold to find. Miners have to look far and wide for new deposits, and they have to dig deeper to find smaller amounts of gold (lower grade deposits). Higher gold prices have not fueled increased supply, despite incentive to increase production. Simply put, there is not enough supply to meet increased invesstment demand. Extrapolate that scenario out as you must.

US Mint has run out on Buffalo gold coins

http://af.reuters.com/article/metalsNews/idAFN2711303520100927

The U.S. Mint has run out of a type of highly pure gold coin it had been selling amid record high prices of gold.

The mint said it will not stock more of the 1-ounce, 24-karat American Buffalo bullion coins.

"The United States Mint has depleted its inventory of 2010 American Buffalo One Ounce Gold Bullion Coins," the Mint said in a statement, seen by Reuters on Monday.

Officials at the Mint could not immediately be reached for comment.