RIM publicly cancelled the BlackBerry Theme Studio v7.1 build to focus on BlackBerry 10 but they were getting close to a release. They realized that the effort to fix the bugs in Theme Builder 7.1 was better spent on perfecting BlackBerry 10 and I have to agree with them. The beta builds RIM was beta testing with key developers have been bouncing around under the radar but BBOS decided to make one of them public. Personally I would not recommend using it to develop themes for sale since I doubt RIM will allow them in App World and the builds I have seen so far have not reached a level that makes themes ready for regular use. ..
If you are still interested in this “deadware” then you can pick up the last beta of BlackBerry Theme Studio 7.1 before it was cancelled at this link