you can get a hunckrow if you catch a murkrow in the eterna forest at night and evolve it.
Murkrow, you can find it in the... ?viridian forest? (not sure what it's called, but for sure in a forest)
You can only find Honchcrow and Togekiss while in the sky, and Togekiss only after you complete the quest to find it.
First of all, you have to clear the game. After that, Togekiss and Honchkrow appears in the sky. Honchkrow is in the area between Aqua Resort and Tilt Village. There is a chance to see Togekiss, Honchkrow, Pidgeot or Skarmory. Only one of them appears to the sky. I recommend you to use charged Latias/Latios sign so you can catch it. Hope this help!
When you face him in veilstone city, he will have Murkrow-LV 40 Sneasal-LV 43 Golbat-LV 40 When you face him at the spear pillar Hunchkrow-LV 45 Weavile-LV 47 Crobat-LV 46 Gyarados-LV 45