That depends solely on the Pokemon game you are playing, Dark type Pokemon were first introduced in Generation II or Gold and Sliver
This is a list of the every dark type and where to catch them in Black/White 2
Umbreon- Obtain Eevee and level it up with max happiness at night
Murkrow- Find in a hidden Grotto inside Pinwheel forest alternatively if you have Black?White 1 go to the abundant shrine and you have a 5% chance of finding a wild one
Sneasel- Found inside the Giant Chasm via the cave,plains, or inner cave.
Houndour- Only found in Dream World or Via Trade
Houndoom- Same requirements as its pre-evolved form Houndour
Tyranitar- Found at Route 15
Poochyena- Dream World or Via Trade alternatively can also be found in a Pokemon Swarm in White version at Route 9 but that being said takes a lot of time
Mightyena- Evolving Poochyena is the only way to obtain Mightyena other than Via Trade
Nuzleaf- Found at the Nature Preserve which is only accessed after seeing every Pokemon in the Unova dex
Shiftry- Also found at the Nature Preserve but only in shaking grass and you only have a 5% chance of finding it. Better off using a leaf stone to evolve Nuzleaf
Sableeye- Found Via Dream World or Trade. There exists an in game trade with Curtis but this only applies to Female players
Carvanha- Fish at Village Bridge
Sharpedo- Fish at the rippling Water spots at Village Bridge
Cacturne- Only found at Reversal Mountain during a Pokemon Swarm
Crawdaunt- Surf or Fish at the rippling water at Route 3 or Straiton City for a 10% chance to catch it
Absol- Found at Route 13 and Route 14
Honchkrow- Evolve Murkrow using a Dusk Stone
Stunky- Found only Via Trade or Dream World
Stunktank- Evolve Stunky or Trade
Spiritomb- Dreamworld or an In game trade from Yancy or Curtis depending on your characters Gender
Drapion- While there is no way to directly Catch Drapion you can evolve his pre-evolved for Skorupi at level 40, Skorupi is located at Reversal Mountain
Weavile- Evolve Sneasel at night while holding the Razor Claw
Darkrai- Darkrai is a legendary Pokemon and not one very easily gotten via Trade, you can search for one but it may take a very long time
Purrlion-Route 19 and Route 20
Liepard- Route 3,5,9,16 and the Dreamyard
Sandile- Route 4, Desert Resort and Relic Castle
Krokorok- Relic Castle
Krookodile- Evolve Krokorok or obtain via Dream World
Scraggy- Route 4 and Desert Resort
Scrafty- Route 1,15,18 and P2 Lab
Zorua- Gift from team Plasma in Driftveil City
Zoroark- Evolve Zorua
Pawnard- Route 9
Bisharp- Evolve Pawnard
Vullaby- Route 23 Black 2 Only
Mandibuzz-Route 4 (Thursdays only) Black 2
Deino- Breed Zweilous or alternatively catch from Black/White 1 Victory Road
Zweilous- Victory Road
Hydreigon- Evolve Zweilous at level 64
Ghost-type Pokemon are weak against Ghost and Dark-type moves.
Liepard is a Dark type Pokemon.
Mightyena is a Dark type pokemon.
Since mismagius is a ghost type Pokemon counter with a dark type Pokemon like honchkrow.
Scrafty is a Dark and Fighting type pokemon.
any Pokemon that is a dark type any Pokemon that is a dark type
Dark type pokemon didn't appear until Johto
Yes. Sableye is a dark and ghost type pokemon.
Ghost-type Pokemon are weak against Ghost and Dark-type moves.
Dark-type pokemon are resistant to Dark and Ghost moves, and are unaffected by Psychic.
dark type Pokemon are said to be created after team rocket. some dark types are umbreon and tyranitar
Umbreon is a Dark type pokemon.
Zoroark is a Dark type pokemon.
Purrloin is a Dark type pokemon.
Liepard is a Dark type Pokemon.
Poochyena is a Dark type pokemon.
Mightyena is a Dark type pokemon.