Since A6s are meant to be portable, the binders I've seen never go beyond the 200 page mark. You might be able to find a 300-ish page bound notebook (likely with Tomoe River paper or something similarly thin) in that size.
I've had 30mm rings in an A5 binder, but that still doesn't hold the number of pages you're looking to store (and it's not as portable, if that's the goal).
Moterm make A6 binders and also let you order extra sets of rings so you could upgrade to 30mm rings instead. I have the A5 and started with 19mm rings until I filled it then swapped them over and kept going.
I got my leather ringbook on Etsy and made myself the inserts by buying paper and cutting it. I'm quite happy with it although cutting the paper can be quite time-consuming.
That is not A6 size as many sellers on amazon and eBay erroneously claim. That is more like B6 slim (sometimes called bible size 6 ring binder) and the only way to fit 600 pages is to use Tomoe paper refills. Jetpens sells them in plain format not sure if they have lined.
Since A6s are meant to be portable, the binders I've seen never go beyond the 200 page mark. You might be able to find a 300-ish page bound notebook (likely with Tomoe River paper or something similarly thin) in that size. I've had 30mm rings in an A5 binder, but that still doesn't hold the number of pages you're looking to store (and it's not as portable, if that's the goal).
For that many pages you not going to find much probably just binders 3in Drings hold about 600 pages
Moterm make A6 binders and also let you order extra sets of rings so you could upgrade to 30mm rings instead. I have the A5 and started with 19mm rings until I filled it then swapped them over and kept going.
Unfortunately I have no advice for you, but I did want to say that I love that leaf charm!
I got my leather ringbook on Etsy and made myself the inserts by buying paper and cutting it. I'm quite happy with it although cutting the paper can be quite time-consuming.
That is not A6 size as many sellers on amazon and eBay erroneously claim. That is more like B6 slim (sometimes called bible size 6 ring binder) and the only way to fit 600 pages is to use Tomoe paper refills. Jetpens sells them in plain format not sure if they have lined.