Just to clarify for clarity's sake :D, Paul's Thumbies are not shifters. They are adaptors which will work with 9-spd Shimano bar cons to create thumb shifters.
WebCyclery sells either one or the package but I'm sure wherever you bought the bars will have them also. Note that two clamp sizes are available.
http://www.webcyclery.com/product.ph...5&cat=0&page=1