This is a release done by myself, Anonymous K, Choutte and Darkrufy a bit ago(4/22/08).
Though not Getter Robo related, this is Go Nagai's masterpiece that deserves to be read by all.
Links for all volumes:
1, 2, 3, 4, 5
If you haven't read this, download it now. This comes with my highest recommendation.
Edit: Volume 4 link updated.