This are four different countdown sounds for orbiter. They're all going fromm T-10 to about T+5 seconds
STS-121 countdown
STS-114 countdown
New Horizons countdown
Mars Reconnaissance Orbiter Countdown
Just rename the file, you want in countdown.wav and put it into yor base/sound/vessel directory.
If anyone of you want the countdown from about T-60s to T+120s or even a whole launch video of the launches above, just send mei a mail!