On my boat, it's the Beckson Vent-O-Mate (C-6SS). There's a picture on the company website:
https://beckson.com/vent.html. You could contact them about parts.
I replaced mine in 2018. I got it from www.marineoutfitters.ca. It doesn't look like they sell parts kits though.
Contacted Beckson.com, they are manufacturers of the vent.
They have a part kit C-6D that replaces the original plastic parts.
Waiting to here where I can order from, not listed on Amazon or at West Marine.
$40 US + shipping from Beckson for the vent plastic parts. They advised try Fisheries Supplies in Seattle.
There you go. I just bought a new in box complete Beckson vent from Craig's for $12 CDN
Just replaced foreward hatch vent. Nice that the same vents are still made. Pretty easy job however, the new screws are a different length then what was there previously and some of the plexiglass has chipped away. The newer Vent-O-Mate has very minor improvements over the old one. The old plastic pieces pretty much turned to sand when I touched them.