I didn't see this spelled out explicitly in walkthrough or quick google search, so I'll write it up here for those interested. There is a secret area of the Zerard Starship factory which is accessible after the factory is cleared. You can see it clearly if you wait until you find every transporter on the planet, which will show this area along with the rest of Zerard.
After you've completed the factory portion of the story , you can go back to Assembly line 1 . Go to the northeast (top right) upper level, where there is a previously sealed door and a woman who will tell you that Daytron employees are being held by renegade robots past that door. There are 6 robots in all, in addition to the normal random encounters.
Enter the area, which is distinct from the rest of the factory by red lighting. You will eventually encounter 3 groups of 2 Assault Walkers each. Just walk around in the area until you encounter them, though there will be encounters with ordinary creatures as well which don't count. Each of the walkers is equipped with a barrier which must be broken by Jaster's barrier break shot or a burning strike technique.
After you have defeated the three groups of assault walkers, three chests will appear in the maze. They will contain a Zenon D pistol for Jaster, A Brave Spirit axe for Deego, and Zeranium Armor for Steve.
It took me awhile to remember where all this was.
Have fun!
Respectfully,
Brian P.