Itoya makes a 13x19 for a reasonable price ($30 ??). Sort of a generic binder with fixed/bound plastic pages with 2 prints per page. Nicer ones with zippers are around $100 in that size.
However, if you want the odd size of 12x18, you may have to go with custom-sized one from these guys in NYC: Brewer-Cantelemo Custom Presentation Books
Whatever you do, make sure that the pages will fit if you use a thicker and heavier paper. I have a Florence brand one in 17x22 and thick papers are very hard to slip into it and may stick out a bit on the end too. They need another 2-3mm, imho, in size. Their customer service isn't too hot either vs. Prat.
Prat also makes various books, but they are fixed sizes like 13x19 as are Florence and Itoya. Not cheap though.
Some of the fixed-size ones can be cut down to size with a hot knife (or a wood-burning iron or soldering iron with a blade tip.) on a glass surface with a metal straight edge. It will seal the edge. I'd only attempt it on removable page cases/binders though and not fixed ones.