Quick release plates aren't quite as standard as the first answer suggests.
A lot of (pricier) brands use the Arca Swiss system. If you have a quick release clamp like that, you can order a universal plate or a custom plate that's molded to fit your specific camera from companies like
http://www.kirkphoto.com/Quick-Release-Camera-Plates.html and
http://reallyrightstuff.com/QR/04.html
Otherwise you might have to buy a replacement plate from the manufacturer of your tripod. See if you can order something from their website, or have a look if they have something here
http://www.tripodquickrelease.com/ or here
http://www.adorama.com/catalog.tpl?op=itemlist&cat1=Tripods&cat2=Quick%20Release%20Systems%20%26%20Plates or here
http://www.bhphotovideo.com/c/buy/Quick-Release-Systems/ci/4925/N/4289936034
In the mean time, perhaps you can unscrew the quick release clamp from your ballhead/ pan-tilt head and screw the camera directly to the tripod.