If you're planning to buy gold at Costco's warehouse stores, you may need a backup plan. Here's where else to look.

There are plenty of items to load up in your shopping cart at Costco -- but gold bars shouldn't be one of them.

Costco appears to have found a revenue mine with sales of gold bars, as a survey found that some warehouses are unable to keep them on shelves. Bloomberg found that 77% of the 101 stores it surveyed in the first week of October had sold out of the bars,

Spot gold has jumped nearly 30% this year, successively hitting record highs. Its ferocious rally makes it not only one of the best-performing commodities, but also means that metal has

The Swiss-made bars are only available to Costco members, whose annual fees range from $65 to $130. Made of 999.5 pure platinum, the bars are non-refundable and limited to one transaction per membership at a maximum of five units per order. They are only available online and can’t be delivered to customers in Louisiana, Nevada or Puerto Rico.

Gold’s increase is due to its reputation as a safe asset during economic and political uncertainty and its role in protecting wealth. Last month, gold prices went above $2,600 an ounce, helped by the Federal Reserve’s rate cuts, as gold usually rises when rates are low.

The 1-ounce platinum bar sells for $1,090. Sales of gold bars on Costco's website have previously sold out in minutes.

In a striking display of shifting consumer behavior, Costco Wholesale gold bars are disappearing from shelves faster than they can be restocked. During the first week of October,