how do I change the number of nodes that the admin layout shows?
You could create a nodes view of all your nodes. Set the pager to whatever number of nodes you want to view, and put various exposed filters on the View to help you find the content you need.

You could also access your database directly. Depending on your hosting provider, you probably have access to some sort of database interface. PhpMyAdmin is very common. If you go to the nodes table, you can view as many nodes as you'd like and figure out the NID you need to pull up the node. Clunky, but it'll work.

There's an old doc page for Drupal 6 regarding this same issue, but based on some of the comments, I don't think it'll work for D7. Worth a shot, though.