If your Git repository hosted on Azure-DevOps (VSTS) you can retrieve a single file with Rest API.
The format of this API looks like this:
https://dev.azure.com/{organization}/_apis/git/repositories/{repositoryId}/items?path={pathToFile}&api-version=4.1?download=true
For example:
https://dev.azure.com/{organization}/_apis/git/repositories/278d5cd2-584d-4b63-824a-2ba458937249/items?scopePath=/MyWebSite/MyWebSite/Views/Home/_Home.cshtml&download=true&api-version=4.1