In some versions of Domino (4.6.x) we've identified a bug which prevents projects owned by organizations from showing up when users are trying to import them. This is scheduled to be fixed in Domino version 5.2 an we apologize for the inconvenience.
In the meantime, please try adding yourself as a collaborator to the project (even if you are part of the organization which owns the project). If that doesn't work, please try to fork or copy the project, then import the forked/copied project as needed.
If you're still having trouble after trying the above, please reach out to support.