[Jotaku]

They spawn at random chances on all maps. So there is no such guaranteed places to farm them. You just have to farm in any mission except the very first mission (I haven't seen them in that map) called Aogiri Tree Hideout. Also avoid farming them in Disposal Facility because that map is very hard to farm alone, although there exists a chance to get Kisho Arima. 

If you need Kishou Arima, play as Ghoul on hard campaign.
If you need Centepede Kaneki, play as CCG on hard campaign.

Additionally, in the map named Tokyo, I have seen Centepede Kaneki.

Make sure you check "Obtainable Material" section because it tells you if there exists Kihsou Arima or Centepede Kaneki (however, for centepede kaneki, it just shows "Kaneki" material, which you get the same material for defeating normal Kaneki. But still there exists a chance that centepede Kaneki will appear).

[Scoobert2000]

They spawn at random chances on all maps. So there is no such guaranteed places to farm them. You just have to farm in any mission except the very first mission (I haven't seen them in that map) called Aogiri Tree Hideout. Also avoid farming them in Disposal Facility because that map is very hard to farm alone, although there exists a chance to get Kisho Arima. 

If you need Kishou Arima, play as Ghoul on hard campaign.
If you need Centepede Kaneki, play as CCG on hard campaign.

Additionally, in the map named Tokyo, I have seen Centepede Kaneki.

Make sure you check "Obtainable Material" section because it tells you if there exists Kihsou Arima or Centepede Kaneki (however, for centepede kaneki, it just shows "Kaneki" material, which you get the same material for defeating normal Kaneki. But still there exists a chance that centepede Kaneki will appear).

Made a guide of which map would be best to fight Centepede Kaneki. Best Map to fight Ken Kaneki -Centepede- Accomplish No. 92/184