How to replace or cover a hole left by kitchen fan that vented to nowhere?

I removed my old exhaust fan, and in my naivety I disposed of it prematurely, thinking that I would be able to find a drop in replacement. Either my Google-fu is failing me, they don’t make the size fan anymore, or it was a hack to begin with.

A couple of notes about this opening:

• The size of the opening is roughly 9"x 9"
• It looks like there is some sort of cover or door at the very top, and it appears that the cover is designed to open, but I don’t know how to confirm this.

My questions are:

1. Can anyone provide any information on this type of opening?

2. Is there a fan that I can install in this opening? If so, what type? All of the kitchen/bath exhaust fans I’ve seen are made to install into a round duct coming in from the side. If so, what type of fan should I be looking for?

3. If not, What are the alternatives beyond a custom grille to cover it up?