You can contact Tim at
GS Astuto. He does rentals of good road bikes but it's expensive, I believe. Probably not a cost you'd want to pay for multiple days. Honestly, based on the cost for renting something decent, if you have Bromptons you should probably just bring those.
Edit: I've never heard of these guys before, but here's another option that just popped up in my search:
https://globalwheels-japan.com/