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

Retailers like Costco and Walmart are selling precious metals including platinum bars, driving a new demand for precious metals.

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, the financial news outlet reported Monday.

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

Newmont Corp., one of the largest mining operations in the world, announced early Wednesday it will be minting a traceable gold bar through MKS PAMP, of Switzerland, using Provena