Unfortunately, the 2007 Chevy Silverado does not have Bluetooth capabilities—in fact, General Motors would not add Bluetooth to any of their vehicles until the 2009 model year, due to the fact that they already offered OnStar, which had similar features.
If you can’t find an adapter, you may have to replace the radio/stereo head altogether if you wish to add Bluetooth to your 2007 Chevy Silverado. However, be warned that a new stereo unit + installation will be much more expensive than a Bluetooth adapter, usually between $200-$500 for the part alone.