I thought I should add the game to steam but can't find the key anywhere in my account page or the games download page. I know I'm probably being blind but if anyone could point my in the right direction that would be great.

Found it through the original purchase email, is there really no way to view unclaimed keys through either the itch app or the web interface?

I'm not certain, but I believe the key can also be obtained through the download link at the top of the page.