They're hard to find. I had to get one one from the USA....
The cover is p/n 1326876-8
The 2 screws to hold it on are p/n 1357937-0
GCP.se has new covers for 93 SEK plus shipping.
They don't stock the 2 screws, which are M6 sized, but Marine Direct Australia has them listed for $1.23 each.
https://www.marinedirect.com.au/1357937-volvo-penta-australia-screw