There is only one legitimate way to complete the Sinnoh Pokedex. To complete the Sinnoh Pokedex you must trade for the missing Pokemon with Pokemon Diamond, Pearl or Platinum.
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You get a ticket to sinnoh and and pokedex entries are expanded
Please see the related link for a complete Pokedex from the Sinnoh region.
First complete the sinnoh pokedex, 210 Pokemon
Just go to Pokemon platinum central and click on pokedex and it shows you where to battle all the Pokemon in sinnoh.
Pokemon #80 in Sinnoh pokedex is Barboach.