I picked up a 2000ish hyside 14 footer over the weekend and it needs 3 thwarts. It's pretty pricey to buy them new from the factory, so I figured I'd try here first. Let me know if you have any laying around!
Call Down River Equipment. I needed a thwart for our 14' DRE (which were made in the same factory with the same materials and dimensions as a Hyside). They had a box they were able to look through and find the size and even color I wanted! It was lightly used, but made it quicker and better price than new through Hyside. I wanted gray and they had a few others that were gray and similar size at the time. Not sure about other colors.