Reddit mentions of CLEARPRINT 1000h Series Vellum Grid Roll Size: 2" H x 2" W x 42" D (10102158)

Maruman makes a paper that is supposed to be "foldable" ruled paper to fit a B5 binder, but when it's unfolded, it's B4 size. I haven't used this paper, but I have used other Maruman products and never been displeased with their stuff.

JetPens has it w/ US shipping, or if you have a Kinokuniya bookstore near you, they carry Maruman products there.

Otherwise, the next closest within US availability: graph paper, but to eliminate all the horrific garbage you've probably been encountering, it has to be clearly marked on the packaging as having "non-photo" or "non-reproducible" grids. This means markings will be faint, and also means the paper will not suck because it's being marketed to artists and for drafting purposes. It will also come in sizes larger than Letter. Brands that will fulfill all of this include Bienfang, Staedtler, Alvin, and Canson. You may be able to find Bienfang at crafting stores, Staedtler I have seen in the drafting section of office supply stores, Alvin and Canson, you'll more than likely have to find at an art/architectural supply store, or via the internet.

See also, thicker vellum paper is made with non-repro grid lines, and comes in a huge variety of sizes including rolls that can be cut to size ...but...that is probably overkill as the last time I used a giant sheet of vellum was in perspective class to create the perfect drafted drawing, not as a notebook. (they do sell vellum notebooks but, they're tiny )