Well, you can always fold the big ones.
Just get a couple of spring clips, use one or two to keep it folded up the way you want.
Or you can always ask a print or copy shop to print out the size you want, just give them the PDF files to print from. They probably won't have water-resistant stock, so you might want to buy a ream of that in the size you prefer. Most paper merchants can supply you a few
sheets at no charge, to test different media and see which one takes the inks well. A light dusting of matte
varnish or
cheap hairspray also helps seal the inks in. (Honest.)