I asked this quite a while ago on Allen's forum, and it's still a mystery to me.
"Been missing for 25 years now, which is ridiculous.
How hard could it be to get these items?
I find it hard to believe that they exist for no other purpose or application other than this.
They are a pair of tiny white bushings that plug into the hole on each side of the bottom of the louver where the latches go.
It's all detailed in an exploded view diagram in the MPC which I'd post if my dvd worked in Vista."
Might have to break down and buy an NOS louver kit, and just sell my current setup.