Much to learn you still have...
When it comes to the bare-bones essentials of q3engine mapping, there are two file formats that stick out: .map and .bsp. foo.map is the editable format that you open up with some flavor of qeradiant (be it JK2Radiant or GtkRadiant or what have you), while foo.bsp is the compiled binary file which is readable by whatever q3engine game you are playing. This situation is roughly analagous to foo.c, the source code to some program, and foo.exe, the compiled binary executable of that source. You play around with foo.exe for a while and want to make some changes--tough patooties. Unless you have access to foo.c, you are S.O.L. Same holds for q3engine maps: if all you've got in your hands is a .bsp, there is no "editing" to be done (save the potential for severely breaking it with a hex editor or something). And no, sorry, Raven hasn't released the .map file for the level you seek.