Is there a git command that can output for every commit:
git ls-tree -l -r &l
You can also get a list of all commits (including the dangling ones) with:
git log --walk-reflogs | grep -E -o '[0-9a-f]{40}'
Include this line in the settings for a new view in gitk (in the last input field, the command to generate additional commits) and you will get a tree that also shows the 'forgotten history' of the project.