This is a general linux problem: how do I install software X if it’s not available into Linux distro Y.
Since GNU Privacy Assistant is not on the official packages on fedora if you want these requirements, you’re probably better of switching the template of that AppVM to debian, where it is avalilable as well (not only whonix).
So check if there is no program that you can’t do without on fedora and consider that change.
Unfortunately there is no easy way around it. Here are some summaries of the nighmares
- download from website - you’ll have the pain of manually verifying the package signatures. Plus, regularly manually check for updates.
- build from source - verify signatures and regularly rebuild.