I've read about iguanas in Florida who survived snowy periods. One quote I remember is "We go and pick them up (while they are motionless and stiff, laying in snow.)". They become active again when they've warmed up.
I know how upsetting it is when we loose an ig.
There is one place in the kitchen where he could be hiding, if there are inside corners in the cabinetry. Go to the inside corner, down on the floor. Note that the corners have what are called "Toe kicks", the four inch pocket at the bottom of the cabinets. Feel under the kick, looking for an opening that is in the ceiling of the pocket. They are easy for igs to find.. They get in them and lay there quietly for days.
Note that when you are searching for him in trees, that iguana have an automatic hiding trick, which is moving their bodies to the back of the trunk/branch, and stick their head around just enough to watch you. What you see from the ground is just the head.
I also read in this forum about another missing ig. The owner found it in the innards of an old-fashioned stove. He couldn't reach it. So he left it's favorite foods, and water, on the floor and waited. He saw it was coming out at night to eat. So he set up a CCTV in the Kitchen so he could know when it was out, and dashed in to pounce on it, and luckily caught it.
Check all the animal rescue places near you. Some are run in private homes, So ask around.