Another thread pointed out some current Wilderness Systems kayak models (Tsunamis) are available again. I got curious and followed the link and found that the current Wilderness Systems website appears to have more spare parts available than I remember them having in the past. Specifically, they always listed the oval rear hatch cover for the Tempest 170 as “not available”, and they directed you to see if any retailers like topkayaker had them. Now, the website shows it as available for order. So, if you’ve given up on any Wilderness Systems spare parts, it might be worth trying again.
Instead of going through parts a page at a time (it’s slow), you can use the search function on the home page. I searched for “hatch cover” and it took me to all of the hatch covers on the parts page: