TacticalDanI'm debating buying this, but if I do get it, I'll put in a Seven Seas Writer or Standard, sold by Nanami Paper. These are a bit expensive (I'm a fountain pen user and these notebooks have excellent quality paper for fountain pens--the mystical Tomoe River Paper). You could check out jetpens.com or gouletpens.com for other notebooks of the A5 size.
TacticalDanI read [somewhere] that the Clairefontaine Collection 1951 Notebooks
search
are good replacements and work very well with our fountain pens. There was a sale of these not long ago and I gabbed 5 especially for this leather journal cover.