The weblogic_sp.jar file is distributed with a WebLogic Server service pack, if you have one. It is there to supercede any WebLogic classes on the CLASSPATH, if necessary. It is perfectly normal for you not to have this file. I the future you should post WebLogic questions to the WebLogic Forum.
If u installed WL 6.1 Service Pack then weblogic_sp.jar file comes along with this Pack. Or If u have WEBGAIN Studio 4.5.2 then the file is there in the path specified in the SETENV.CMD file. But in the case of WL7.0, it has only weblogic.jar file in \lib directory.