A few years ago, when I first came across it, it was hard to find a notebook that I liked that contained Tomoe River paper.
It’s thinner than any other paper, it’s strong, and it doesn’t bleed through. One of those “you believe it when you use it” things.
My best option, one that I still use, and can recommend is the “SevenSeas” notebook from NanamiPaper.
If that sounds obscure, it’s because this used to be the only way: an “independent binder” procuring the paper, and assembling a notebook.
However, it is much easier to find alternative today.
JetPens carries an alternative, the Kanso Noto (320 pages for $20)
GouletPens carries another alternative (160 pages for $16)
More than any of this, searching on Amazon (the very definition of mainstream today) shows a bunch of results (will not link to any here).
No more excuses not to try out this pretty remarkable paper 🙂