I would probably just use a stack of soft rubber washers or something to fill in the gap if you can't buy it. That's just a vibration dampening mount so as long as the box can move around a little bit it should be fine...
Wondering being that the line extends from the bolt at top of page if you could call Toyota parts and see if it comes with that particular bolt? Appears it's part of the air cleaner assembly though and may not be serviced separately. Not sure if this is the same thing but might work: