Actually its a custom cable by htc. i dont believe just any micro to composite will work, since the video isnt actually output through the usb but through 7? more seperate pins that are a little tougher to spot. You may be a able to find a third party built one but your best bet would be from htc or verizon.
heres a thread dedicated to it. It even explains how to build one.
another thing to keep in mind is currently no AOSP roms(such as CM7) support tv-out