Definitely bring sufficient from home. We were caught out in a snow resort area and had very limited Panadol left after everyone had had a string of mild colds, despite packing what we thought would be sufficient. We tried to get some at Sapporo station before heading off but couldn’t locate any. The store at the snow resort also didn’t stock it, and we were also told that none would be available via the medical services at the resort either (!!)
In short, none was available via the usual routes you’d expect if in Australia. No doubt it would be easier in a city, but you don’t want to be unexpectedly caught short.