Here are some sounds I made myself for unit makers who want custom sounds for their creations. They are in .wav format, so you can't use them "as is" (civ3 sounds are in 22,050 Hz, 16bit Mono, 43 kb/s), you need to convert them (or ask me any format you need). This is the first wave, I'll put some more if people want more. I could also make combinations of different sounds so they match with your units, just put it in a very simple language so I can understand what you want.
Some samples (mostly mechanical sounds made with... my old car!)
http://forums.civfanatics.com/downloads.php?do=file&id=8053
Here are some more sounds: SF ones. I think they must be hard to find, although they are quite easy to produce. I'll put them in Civ format as soon as I can. Hear them here
Edit: missing links fixed August 01, 2008
Some samples (mostly mechanical sounds made with... my old car!)
http://forums.civfanatics.com/downloads.php?do=file&id=8053
Here are some more sounds: SF ones. I think they must be hard to find, although they are quite easy to produce. I'll put them in Civ format as soon as I can. Hear them here
Edit: missing links fixed August 01, 2008