Even the most ardent runway watchers are not sporting Prada’s Fiocco dress this season. The sleeveless dress is a stunner — with a faded green embossed bodice, full wool skirt, and a red doublestitched belt — that can’t be found in Prada stores, on eBay, or even on net-a-porter.com. That’s because the dress never made it to production; It was only a prototype, or sample, for fall 2007.

Today, it can be yours. Prada announced yesterday that it would begin auctioning online 24 pieces from its “prototype collection,” selected by the company’s head, Miuccia Prada. None of the items have appeared or been produced in the colors or materials that will be available through the auction. Most were originally created for the fall 2007 season.

Three items will be auctioned each Monday, Wednesday, and Friday until July 25. The collection includes dresses, skirts, bags, and shoes. Two dresses — the Navy Radzimire and Vanill Flapper — were created exclusively for the auction. Yesterday’s offerings included a quartz mohair coat with a furry sleeveless top. A pair of Mary Jane high heels — in yellow and black — are a closed-toe version of shoes that were eventually worn on the runway.

A line graph on the site charts each item’s progression of bids, making the auction somethingof a spectator sport. Bidders with names such as “princeMonaco” and “von-sudenfed” jockeyed over the opening day’s hottest item, the Fiocco dress. It was going for $385.53 yesterday afternoon and is likely to rise much higher: Prada dresses, the ones that did hit the stores, are sold on eBay and are going for up to $1,850. The proceeds o the sale will benefit Fondazione San Raffaele, a medical research facility in Italy.