Robert's answer is good if the project is large, although you will check a lot of content to get a single file.
If you want to get a separate file from SCM, the Maven SCM API allows you to directly interact with the SCM repository to invoke arbitrary targets. In this related answer, I provide an example of a custom Mojo that commits a single file, if you implement this mojo and change the command from add to checkout you will avoid checking the entire project.
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