You can import any midi, MUSIChtml, or tabs, like power tabs into Guitar Pro 6. So, anything you can find in the way of midi percussion files would work for you.
http://www.tigerbill.com/drumsandmidifiles.htm
http://www.fivepinpress.com/drum_patterns.html
http://www.synthzone.com/drums.htm
You can also download power tabs files from various sources like - http://www.tabscout.com/
MUSIChtml files are used to add sound to web sites so, I don't believe you will find any of these files that you can actually download or use.
However the best way to do that would be to get yourself a midi drum pad and record your own bests directly into guitar pro from the pad in midi through one of your USB ports.
http://www.sweetwater.com/store/detail/ControlPad/
http://www.sweetwater.com/store/detail/MPD26/
http://www.sweetwater.com/store/detail/SP555