A bit of a correction for the TRS-80 Coco ones you found- Galax Attax and Galacticans are clones of Galaxian, not Galaga. There is a game called Galacon that actually is a Galaga clone, however (published by the same company as Galax Attax was).
The only actual Galaga clone:
Galencia 7:35
The rest is just Galaxian clones.
Me, 5 hours later
anyone else here or am I first
Gotta love how the vast majority of Galaga clones in this video are actually Galaxian clones.