I did my portfolio on 11x17 paper, horizontally, and got a nice portfolio book from Lost Luggage. I just checked, and 11x17 landscape is the largest they have. It does look rather nice when opened up. I mixed up the sizes and shapes on each page -- some are full bleed, a few panos that run over both pages, some that have two or more vertical photos, and a couple of spreads with 8 or 10 images.
Now that I think about it, that portfolio is rather old and I need to redo it. (I'm on staff, so I'm not showing it all the time.)
Sorry I can't help with a landscape 13x19 book.