The subject vehicle for this story is a 1990 TBI Suburban.  In stock trim, it has a single air intake snorkel, with a cool air tube that runs from the intake snorkel to a fixture on the core support.  This provides cool, outside air to the throttle body, instead of hot, under-hood air.  To find an intake snorkel and cool air tube that would fit the drivers side, I had to look no further than under the hood of the '91 S-15 4.3L V6 TBI Jimmy that I also owned.  I found a similar rig in the junkyard and snagged the bottom part of the air cleaner assembly and the cool air tube from it.

Next I used a cutoff wheel to remove the air intake snorkel from the air cleaner from the S-15, and to remove a similar sized piece from the drivers side of the air cleaner from the Suburban.  A few minutes with the welder and I now had a fairly symmetrical dual air intake that fits quite nicely under the hood of the Suburban and almost looks factory. 

From the picture, you can see why I said it's only fairly symmetrical.  Since the brake master cylinder is in the way, the S-15 air snorkel and cool air tube are made differently to provide clearance.  If you look closely at this pic, you'll also see that the S-15 cool air tube is just a bit too short to reach the core support.  My plan is to either splice part of another S-15 cool air tube into it, or find another cool air tube that is long enough.  The Suburban core support already has knock-outs on the drivers side of the core support for another air intake.  Just knock them out and in comes more cool, outside air for the engine.  Not bad for around $5.

While the parts used here may not match up with your particular vehicle, I sure hope that it provides some ideas for you.  Snoop around at your local junkyard and see what you can find that would let you do the same thing for your ride.