Hi Julia,
I also don't have a Mac to test things on, but it might help if you provided some more information about the process you followed. If you provide the info below, the list can probably better help you:
2. Are you using the command:
sudo port install pspp-devel
or the command:
sudo port install pspp
3. Have you successfully installed PSPP on another Mac?
4. This site,
https://lavergne.me/projects/pspp/, says that "GUI programs are in /Applications/MacPorts and command line in /opt/pspp/bin" did you try those two locations?
Hope that helps,
Mark