Depricated Forge Versions

[Thornack]

I have noticed that you cannot install successfully downloaded older src from versions of Forge (from like 1.7.10) and use maven to set up a dev environment which means that effectively you cannot mod older minecraft versions. The build script appears to fail when gradlew is executed due to the external repo's no longer being valid. The message states could not resolve all dependencies, where you get a status code from server 501 https required. Is there a workaround? (and I know the versions are no longer supported but for someone wanting to edit an old mod of mine for an old version of minecraft is it possible?