Too many instruments, not enough space

Maybe I am the only one who hasn't figured out how to do this yet, but I can't seem to figure out how to add together more than about 14 different instrument lines on one score, while still having them all fit on the page. For a symphony such as Mahler's 2nd, which has more than 20 lines, this is not enough. Sure, when I create the new score, I can select 25 instruments, but 11 of them disappear off the page, which is useless. I don't know if there is a way to increase page size or have the "overflowing" lines be put on a second page. If anyone has an answer to this, that would be awesome. Thanks!