Here's the first chapter of Getter Robo Arc volume 2. This is quite a good chapter and the following chapters are even better as the story really starts taking off. Thanks to OtherSideofSky for his awesome translation!
Getter Robo Arc Volume 2 Chapter 7
Also, it seems I somehow forgot to do a full volume compilation of Getter Robo G, so I've added a download link for that. Thanks to the reader who brought this to my attention.
Getter Robo Saga - Getter Robo G