Are you thinking you want to reserve a taxi, or be able to call one to come for you at any given time?
Many independent accessible taxi drivers tend to work on an advance reservation system and may not be able to come when you call (especially weekdays during hospital hours when they are focused on seniors).
Would be happy to look up some for you though! Would you be able to call (in Japanese)? Or would you only like places where you can email them?
Have you tried any of the JpnTaxis? (The ones that look like a London cab.) If you use the GO Taxi app, you can typically specify you want an JpnTaxi (with a ramp) to come and they will arrive within a few minutes usually. I used it a few times in Kyoto this spring and found it very helpful – came quickly, can see location on app etc. The only downside is that if you use a larger power wheelchair (like I do), you may not fit easily. I had to remove my headrest to get in.
I would suggest that, but let me know if you want some other options!