Well, you could post a layout of your room on a website, and we could print it and dowse for the doodie. Other than that, we’re not likely to be of any help.
You have my sympathy, though.
That cat’s a keeper. He fertilizes, he mows; train him to trim the hedges and you can fire the gardener.
It seems to me that there is, in fact, a general GQ (general General Question?) here: Is there a way (method, device, etc.) to locate the source of a particular odor? Judging by the answers so far, it seems that many people just assume that the answer is obviously “no”, but that doesn’t make it an invalid question.
To me, it’s not at all obvious that there couldn’t be, at least in theory, some sort of a device that detected some (settable?) particular odor molecules and computed their relative concentration in the air, and gave feedback when that concentration was going up or down as the user moved it around. Sure, with the air being moved about by the very act of moving the device, it probably would be far from exact, but is there some reason that it would work at all? That it couldn’t give at least some general idea of where the source is, at least giving the user reasonable cause to focus on one area of the room first?
Is there upholstered furniture in the room? The kind with dust fabric underneath it? The kind of dust fabric that cats love to tear a hole in so they can climb up inside?
lieu, when it comes to shit threads, you are once and always the master. 
I think the OP locked the cat in by accident. You know how cats are- they’re always getting themselves into impossible places, and you close the door without realizing there’s a kitty in your closet.
Check the top of the ceiling fan…those frackers can jump and are quite devious…
And if it is there, you’d really want to find it before turning the fan on.
I have a cat who closes doors on the other cats for fun. Seriously. And then they shit under the fridge.
Figure out what the most important, hard-to-replace paper or object in the room is, and then look there.
Hmmm…way to make a guy feel invisible. (See post #5) 
I agree with the dog idea. One of my cats dropped one in my home office with a bunch a papers lying around and whatnot. There’s no way I could find it quickly and it smelled horrible. The dog came in and sniffed it out instantly. Done deal.
This thread sounds like an IMHO thread… What’s the Best Way to Find a Hidden Cat Turd?
Nono, the perfect word play is, “Where (the deuce) is it?”
You should even check the drawers, one of my cats is able to open my dresser drawers and every once in a while they close the drawer, too. I wouldn’t even have known it had been opened if not for all my clean socks on the floor.
In a home office… I’m picturing the cat standing on a file drawer’s edges just to drop one down in/inbetween some files, then shutting the drawer behind him. :eek:
My parents had a cat that had diarrhea behind a desk once, on all the computer cables. Cleaning cat shit off a surge protector is not awesome.
Dogs are probably the best way. Lacking that, I’d start in order of hard to clean places, then move toward more convenient ones.
Then who’s going to f*** my wife?
But would he have filed under T for turd, or D for deuce?
Do you have any shoes laying around? Check in them.
Growing up, my dad was always paranoid about the cat taking a shit in his shoes for some reason.
That sounds like learned behaviour.