I'd like to sync a repository between a corporate Github and a corporate TFS. TFS UI don't support remote repositories on the server.
Is there a way to designate the git repo within TFS as a remote on Github? I know I can sync via a local repo that would list both as remotes, but can this be done without a local one?
Unfortunately, there isn't such an official tool or services. You have to manually do the sync via a local repo as you mentioned.
Another workaround is with help of a special build in TFS, then calling git command during the build pipeline. Detail steps please refer this blog: Keep Git repository in sync between VSTS / TFS and Git. You could also use the Git Tasks in marketplace.
Also reference this article : Sync between my GitHub and Visual Studio Online
You can also submit a user voice to suggest the feature on this site: https://visualstudio.uservoice.com/forums/330519-team-services