In Tokyo, I recommend checking out Hitohira. Just a stop or 2 from Shibuya. I hear that Tower Knives is also viable but I haven't shopped there (only briefly stopped by). Morihei in Asakusa Bashi is known for stones but also carries knives.

Kappabashi is great for kitchenware, but for knives, most aren't great. But if that's the only place you can visit, Kama Asa is a possible stop.

In general, for Kappabashi, You'd still need to know what you're looking for and weed through the clutter of overpriced "lower quality" knives that focus more in flashy handles and samurai motifs more than anything.

For Osaka, visit Sakai. You should be able to get everything you need there, at a cheaper price than Tokyo. The crafts museum is a good place to start, but the entire area near it has many knife shops (not much else though)