For future reference, check the high spots in your house if your chameleon goes missing. They may wander around for a bit on the floor, but in the end they'll always try to climb something to get up higher where they feel more secure.
But while you're looking up high, be careful where you tread. They tend to get underfoot quite easily (because you hardly notice them).
Also, I've notice on the odd occassion when my cham does climb out his cage (usually when I'm doing maintenance or cleaning work on it) he tends to go for the light. That's not actually a good thing, because the light comes from the windows, and if the windows are open, he'll get out into the garden and that's when they become really difficult to find...
So my advice is that if there is any chance of your cham escaping its enclosure (like when the cage is open), keep the windows closed!
But maybe it's time for you to get a mesh cover for that temporary aquarium - you'd hate to lose your cham, or even let it get injured if it gets out and wanders around your house.
Glad you found him this time.