Extra Getter Stories:
Getter Robo Juvenile: https://imgur.com/a/K23Lh/all

Getter Robot one Shots:
Shin Getter Armageddon, Crater Battle (French): https://bato.to/comic/_/comics/shin-change-getter-robo-crater-battle-r21911
Shin Getter vs. Mazinkaiser (French: https://bato.to/comic/_/comics/mazinkaiser-vs-shin-getter-robot-r21769

Raw Getter Robo Anthologies:
Super Robot Wars: Getter Robo Collection: https://imgur.com/a/qree7
Getter RObo Daikessen: https://imgur.com/a/rHe8E 

Complete works of the two Getter Robot Manga series that were made after Ken Ishikawa's untimely demise:

Getter Robo Hien
(scanlated)
Ch01: http://imgur.com/a/Ch1TP
Ch02: http://imgur.com/a/uE5Li
Ch03: http://imgur.com/a/s9O38
Ch04: http://imgur.com/a/RTlVQ
(RAWS)
Ch05: http://imgur.com/a/G2aGF
Ch06: http://imgur.com/a/o07du
Ch07: http://imgur.com/a/fbaHO
Ch08: http://imgur.com/a/qgcXe
Ch09: http://imgur.com/a/3EnBr
Ch10: http://imgur.com/a/RXZrJ
Ch11: http://imgur.com/a/3ZPwW
Ch12: http://imgur.com/a/V1u9x
Ch13: http://imgur.com/a/AyVps
Ch14: http://imgur.com/a/g7QUf
Ch15: http://imgur.com/a/4kdnH
Ch16: http://imgur.com/a/LcXu8

Apocryphal Getter Robo
(Dash)
Ch01: http://imgur.com/a/k2RRm
Ch02: http://imgur.com/a/nrzMd
Ch03: http://imgur.com/a/EkKrt
Ch04: http://imgur.com/a/5AWxC
Ch05: http://imgur.com/a/EZvvR
(Darkness)
Ch00.5-01: http://imgur.com/a/yrIXV
Ch02-04: http://imgur.com/a/o9ERq
Ch05: http://imgur.com/a/B0hpf
Ch06: http://imgur.com/a/nObdB
Ch07: http://imgur.com/a/QuaMH
Ch08: http://imgur.com/a/S6cJb
Ch08.5: http://imgur.com/a/fWLOd 
Ch09: http://imgur.com/a/T8wIJ
Ch10: http://imgur.com/a/saZC1
Ch11: http://imgur.com/a/FxnCQ
Ch12: http://imgur.com/a/zDCFJ
Ch13: http://imgur.com/a/eSv5C
Ch14: http://imgur.com/a/83shU
Ch15: http://imgur.com/a/levMz
Ch16: http://imgur.com/a/hF6Fz
Ch17: http://imgur.com/a/RmUnT
Ch17.5: http://imgur.com/a/dOscS
Ch18: http://imgur.com/a/iYtGh
Ch19: http://imgur.com/a/SsRMK
Ch20: http://imgur.com/a/B5KUs
Ch21: http://imgur.com/a/EkGlS
Ch22: http://imgur.com/a/DFjKL
Ch23: http://imgur.com/a/y8tS7
Ch24: http://imgur.com/a/OeRy4
Ch25: http://imgur.com/a/Iz4nB