They are there in the sound folder. I checked.

The sounds are:
707touchc.wav
707touchl.wav
707touchr.wav

I could not find any mention of them in the sound.cfg so maybe that's why we can't hear them.
I also found that the 727-100 doesn't have anything about landing sounds either. So I need to see if it doesn't have the sound of the tires screeching a bit on landing. But the 757 sound.PW sound.cfg does mention the tires touching down sounds for the 757.

Mark