Lets say that you want some XXX item (pet, transmog piece, epic item, quest item, rare material, rare recepte and so on), but its never on auction house.
Only thing you can do to get it is either be very patient or use real money and transver to the server where the item is. (you can see that on undermine site)
Or you can grid it, buy the cards for real money, buy pet/mount off the pet store and so on.
I myself killed so many mobs in silithus trying to get 1 green item for the last 2 years with no luck. (never on ah either or it shows up when i am not subbed ).
That item is:
Merciless Legguards
http://www.wowhead.com/item=15655
http://wow.zamimg.com/uploads/screen...mal/318766.jpg
What is your item?