I've heard of goheimochi, but wasn't sure what it was... until I saw this thread and then looked it up. Then I saw the picture and realized I've eaten it a bunch of times before.
Anyways, some googling in japanese identified places that sell this.
Asakusa:
https://tabelog.com/en/tokyo/A1311/A131102/13009811/
Hachioji:
https://tabelog.com/en/tokyo/A1329/A132904/13100716/
Nagoya:
https://tabelog.com/en/aichi/A2301/A230105/23009156/
You're looking for something like this (the version from the Nagoya one, photo credit to Tabelog)?
