Dealer is correct.  Nissan is having numerous issues since the recent
move of National headquarters, one of which is getting critical parts
into consumer hands.  

I believe that the 07 Quest uses a different speedo than earlier
ones, so the entire supply is currently going into production in
Smyrna.  In order to get your part, one of the parts analysts in
Smyrna will have to issue a special requisition for it to be pulled
from the production line, then it has to be boxed and shipped to your
dealer.

Just be glad you don't have a Versa.  Some of those folks have cars
down for over 4 3 months, waiting for the parts to be shipped up from
Mexico.

Chuck

Here's a follow up for you.  Won't help much, but at least you'll
know what's happening.

The 07 Quest uses a different speedo, sourced from 2 different
suppliers.  However, all of them must be calibrated and programed by
a 'special' machine at one supplier.  Now get this.  In April, the
"special" machine was "hit by lightning" and was fried.  They have
YET to replace it, although they have said they would numerous times.  
Meanwhile, each speedo had to be calibrated manually (and in cases
like yours, programmed with the correct mileage as supplied by the
dealer), which takes a lot longer and this has reduced the available
supply to a trickle.  All of the speedos are currently going to
production, except for cases like yours.  The dealer has a specific
procedure to get one, but it can take a LONG time (up to 3 months).  
It also depends on the lemon law time frames in your state.  If it
looks like they will have to 'by back' the vehicle under a states
Lemon law, then.... magically a critical part appears, even if it
means removing one from an unsold unit on the lot.

So... now you know and........ Good luck.

Chuck