Here's a description and links from CNET Asia:
USB-powered air darts
Just when you thought it couldn't get any sillier with USB-powered peripherals (the April Fool's joke of a USB George Foreman grill from ThinkGeek notwithstanding), now Marks & Spencer of UK is retailing weapons of mass destruction. Operating the air dart is Q.E.D. Hook it up to your PC, and start firing with the aid of your mouse. All that's missing is a remote control for long-distance stealth firing. Pesky colleagues, bring it on.
Via News.com blogs
Price: 19.50 pounds (US$34) for three darts with cylindrical base and included software
Availability: Marks & Spencer
Device: USB peripheral