My understanding is that you're asking for source code associated with the EGit plugins available inside the MCUXpresso IDE. That should not be difficult to find - see https://git.eclipse.org/r/plugins/gitiles/egit/egit or/and https://github.com/eclipse-egit
Note that Eclipse-related source code is mostly open-source (EPL licensed) and can be easily inspected by browsing specific repositories. However, MCUXpresso-specific components are based on proprietary source code.
Not sure about the actual limitations you met but I suggest you switch to the latest MCUXpresso IDE (v11.8.1 available, v11.9.0 to be announced soon) that also comes with newer EGit plugins.
Regards,
MCUXpresso IDE Support