I don't know if they're quite what you're looking for, but I was able to record a couple of landspeeder effects from the Behind the Magic CD. One is a flyby effect, the other is more of a start-up effect.
I had to record the clips through my speakers (didn't know how to rip them from the CD), but I cleaned them up as best I could. Hope they're good enough quality and that they help you out. They're also in mp3 format -- hope you can work with that (it was that or wav).
speeder effect 1
speeder effect 2
EDIT: I just stitched this clip together from a few separate seconds from one of the episodes of the Star Wars radio drama. If you're looking for a "consistent" speeder sound to use in the background, this may work. I also included another short speeder sound from the same episode.
speeder effect 3
speeder effect 4
If you'd prefer, I could upload the entire segment that I used from the radio drama so that you can edit it yourself... let me know.