GPLv3 directly addresses your question, so no speculation is required. Conveying unmodified code is covered in s4, and conveying other forms than source code in s6. s6 says that
You may convey a covered work in object code form under the terms of sections 4 and 5, provided that you also convey the machine-readable Corresponding Source under the terms of this License, in one of these ways:
d) Convey the object code by offering access from a designated place (gratis or for a charge), and offer equivalent access to the Corresponding Source in the same way through the same place at no further charge. You need not require recipients to copy the Corresponding Source along with the object code. If the place to copy the object code is a network server, the Corresponding Source may be on a different server (operated by you or a third party) that supports equivalent copying facilities, provided you maintain clear directions next to the object code saying where to find the Corresponding Source. Regardless of what server hosts the Corresponding Source, you remain obligated to ensure that it is available for as long as needed to satisfy these requirements.
It seems to me that telling people who download your code that the source is available on github, and providing a link to the repository, satisfies that obligation, provided they are told prominently, clearly, and at the point of binary download. Tucking this notification away in a file buried five levels deep in your documentation, called
wombat_equivalence.tex, will not satisfy this requirement. Note also that if github goes offline or the original author deletes the repository, that's your problem, not your users'.
GPLv2 contains similar language at the end of s3. I'm less sure about MPL but I'd be surprised if it were not also similar.
In passing, I don't quite understand why you think that "the recipients are just "end users"" would make any difference, here. The GPL doesn't distinguish between developers who need source code and end-users who don't: to it, all users are developers in potentia, and are protected accordingly.