It doesnt work simply because not everyone will do it.
You cant do a search of any camp without actually being there in TAU because the numbers can lie easily. Assault groups show up on the same area.
people camping the crappy TAu HNM show up as being in the same zone and I'm damned sure they arent going to announce a TOD or the fact that they're fighitng it in a search comment. There are tons of ways the number of people can get artificially inflated to seem like a camp is overcrowded when noone is even at the merit camp.
Cannon jobs ect going /anon because fucktars keep trying to invite them when they already have a party makes the amount of people lower . Basically the number of people in a zone fluctuates too easily.
The only real way i've found is to send a scout to the camps while i'm searching for the final members or to ask people in those zones.
XI Wiki

