do a Froogle search on Lemond Lewedge and you will find several online stores that carry them. The are tapered from nearly nothing to just over 1mm. You can stack them alternating the taper if all you are correcting for is a difference in leg length.

Edit: Forgot to mention, I use these wedges on my left foot only, don't seem to have any problems since installation. It solved a problem I had with pronating of the knee.