eBay is a good place to start your search for hard-to-find lawn mower items. I've had good luck there. Also, local mower shops that have been in business for years is another good option to explore. I found a rare part for my HR215 HXA at a local mower shop that was sitting on their shelf I'm estimating for 10 years before I bought it. It came from a mower they parted out back then.
Good luck with your search.