[Ohayo Travel]

Both Tokyo Metro and Toei Transportation say all the stations are accesisble.

https://www.tokyometro.jp/safety/barrierfree/progress/tozai/index.html

https://www.kotsu.metro.tokyo.jp/eng/guides/wheelchair/
As for JR train stations in Tokyo 23 Wards, there are a few. You do not need to worry normally.

[Josh Grisdale]

As Ohayo Travel mentioned, you do not really need to worry in Tokyo. But if you are interested you can also check out this website: https://www.ecomo-rakuraku.jp/en

Also, if you Google a station and go to the page for it, they generally have a red line indicating the accessible route.

[Hamsomy3]

Follow-up Question: I’m on a manual wheelchair. I’m afraid that the station might be too vast for me to navigate. Would the staff be willing to assist in pushing me around within the station?

[Josh Grisdale]

They will definitely guide you to your train, and then to the exit after you arrive.

I am a power wheelchair user so don’t need to be pushed, but I don’t see why they wouldn’t help if needed. (I’m pretty sure I have seen them pushing people…)

Of course, they will only help with getting to and from your train, and you would be on your own if you want to do shopping or eat at a restaurant in one of the bigger stations.