The compare Dialog of TortoiseGit is more about File, and, with Git, you have to compare two master
branches (not just two commits of the same branches both pointing to the same SVN central repo)
If you have git directly on the server, you could rebase your master (of the server repo) with the origin/master (the one of the development repo)
Or you can reset your prod master HEAD to the origin/master and add the files, as described here.
But if you have only Git on the development side, which is wise, you can have:
- a cloned version (called "prod1" for instance) of the repo representing one of your production side (prod1/master)
- or a branch within your own repo (called "prod1_master")
In both case, you need to list all files that have changed between prod1 and master:
git diff --list-only prod1/master
git diff --list-only prod1_master
export those files into a temporary directory that you can compress and uncompress on the prod side.