Publiusr, I really don't know what went into the Star Command Defense Drones; given the late-Seventies, they literally could be anything from pure scratchbuild, to converted salad dressing bottles, to modified chair leg attachments. There was a fair amount of vacuform materials used in the interior full size sets of Space Academy (the interior corridor section, the Bridge/Command Deck and the Seeker and Starfire interiors) but whether the model makers had any access to that is yet another thing that I do not know.
Here are some salad dressing bottles that potentially could have served as vacuform bucks; Girards redesigned their classic bottle in 2019, but the prior design was in use from the 1960's - 2010's.