Instrument Cluster

[JB]

About a week ago, my speedo/odometer quit working. It would register maybe 15mph at highway speeds, and at that, it jumps around alot. Around town, it registers zero. CarDics told me that I need a new cluster (I only took it there b/c I don't have time nor the place to try and fix it myself). I thought it might have something to do with the cable that runs from the cluster to the tailshaft. What else could cause it to read incorrectly?

Also, if I need a new cluster, where can I get one besides a junkyard? Will I be able to have the odometer on the new one set to the correct miles? The truck's old, so I don't think it would matter messing with the miles.

Thanks

edit: Actually I really just need the speedometer head. If nayone knows where I can get one, let me know. Thanks.