Hi--
Check out
MacTracker. It has startup chimes for various Mac models.
To get to the chimes, download the app. Right click on the application icon and choose "Show Package Contents" from the contextual menu. Burrow down through
Contents/Resources/Chimes.
The only other way I can think of to get the sounds would be to hook your computer's audio output to another computer's input, then reboot and record the sound (that's probably how they got those sounds for MacTracker).
charlie