You could probably adapt a skirt from another model or manufacturer. I doubt the lack of this skirt will cause any problem. The actual purpose of this part I believe is just to keep the glass from hitting the launch ramp and/or rattling. I wouldn't worry too much about it.

I rarely see Daiichi spare parts turn up, but I do see whole machines turn up if you want to cannibalize one.

You could use another hopper altogether and make it fit or just use something as simple as cardboard the replace the missing side. Broken hoppers seem fairly common since they stick out.

A nice, clean machine you have there!