7 Months Ago, KXTV says (in Game Guys Review: Nyko's Metal Pedal Accessory)  CA - Barry White
The Metal Pedal is a replacement foot pedal for the drum sets of both Rock Band and Guitar Hero World Tour. It even comes with an adapter so that two pedals can be used as a double-bass, but Rock Band 1 gamers will find that their drum set is not ...

And Gizmodo.com says (in Nyko Metal Pedal Review) Also, if you play both Rock Band and Guitar Hero, the cross-compatible hardware plugs into both drumsets and is toggled with a simple switch. I could see where using the same bass drum pedal for both games could be beneficial if you were a real score ...

8 Months Ago, Jeff Atwood from Fake Plastic Rock says (in Dual Drum Kick Pedals for Rock Band and Guitar Hero) On the Rock Band side of the fence, I was surprised to discover that Harmonix now has an officially blessed dual drum kick pedal solution too! You can buy an add-on kick pedal for $24.99.

The only place I could find the pedal for sale is at GameStop, as the Universal Rock Band Drum Pedal.