Where to find farfetch'd ?

According to everything I know you should find him there, unless he isn't in the entire country. I heard about a snorlax event on japan, if it is true you should stay there a little longer.

When I was there over New Year, I probably caught 5 or 6 during the three weeks I was there. Most of the time that I caught them was in urban areas (my family lives on farmland) so I'd guess I saw one every couple of days when I was in the downtown areas. If you aren't already in a busy area, try that.

Good luck!

He used to be frequent in Hong Kong but now after the update I saw him much less than before. Nevertheless he still exists, and I have encountered a few in my area.

I'm from Asia @L31 but still missing all Regional ;(

If it is following the same pattern as Mr.Mime, it means that these regional exclusives have had their spawn rates reduced. They are still out there, but not many. For about a week in Europe I have found only 5 Mr.Mime.

I've been playing in Tokyo since last summer and I saw 20, so not that common.
Advice: go to odaiba, I saw one or two there last time and there's a lot of uncommon Pokemons there