We saw the potato head parts in several places while we were down there earlier this month, but Once Upon a Toy in Downtown Disney seemed to have a particularly good selection.
We have a "head" already, so we just stuffed the box with parts and got tons. My hubby looked at me incredulously as I was stuffing yet another piece into the box and asked if I was the same woman he knew who hates (HATES) toys with pieces because I always end up stepping on them, having to clean them up etc. I can't explain it, there is just something satisfying about getting the little plastic mouse ear pretzel into that "full" box of potato head parts!!!