Ominous Cloud travels with the circus. He'll be in whichever nation is first for conquest results. If two nations are tied for first, the circus won't appear. Here are Ominous Cloud's positions:
Bastok Port: L-8
San d'Oria South: H-9
Windurst Woods: H-10
Trade him up to 7 stacks of ninja tool at once, and a wijnruit for each stack and he'll bundle them so they'll be stackable.
Wijnruits vendors can be found here:
http://ffxi.allakhazam.com/db/item.html?fitem=1938