Haunter, the ghostly evolution of Gastly, is able to be captured from within the Dusk Factory, East of Fall City. Search the rooms deep within the Dusk factory and you will soon find it. You will need to shut down the factory first, causing the departure of the Go-Rock Squad and subsequent abandon of the factory. This will leave dark and desolate rooms where Haunter like to lurk.
Get a link cable and trade/receive a Haunter.
The Ghost-type Pokemon in the HGSS Regional Pokedex are: Gastly, Haunter, Gengar, Misdreavus, and Mismagius. The Dark-type Pokemon are: Umbreon, Murkrow, Honchkrow, Sneasel, Weavile, and Tyranitar.
pewter city.
no yo can't find it you have to trade it off another Pokemon game.
black stone
Trade Haunter and you will get a Gengar.
Evolve a gastly that you can catch in the sprout tower
Via trade.
Kadabra, machoke, haunter 'Just trading' - Kadabra; Machoke; Graveler; Haunter.
forest at night
You trade it at a high enough level
Gengar is a ghost-poison type pokemon that evolves from Haunter.
Ghastly evolves into Haunter at level 25. Then Haunter evolves by trading.
you can't find haunter in Black
Route 8 Safari Zone (Nighttime)
look in the Pokemon tower in lavender for haunter. note, haunter is hard to find in the Pokemon tower
Haunter evolves by trade