Single-user mode not allowing write access

I'm trying to copy some files from Single user mode to an external USB but I'm having trouble. I can't use the terminal in another account because it's not an administrator account and it's not in the /etc/sudoers file. I need sudo because these files contain the password for a specific user who forgot their password. The path for these files are /Volumes//var/db/dslocal/nodes/Default/users/.plist. I need to mount my usb first to actually put the files in the drive. To do that, I need to make a new directory and mount the drive there using the mount command. But for some reason, even after I run /sbin/mount -uw, I still get an error saying that the root filesystem is read-only. Does anyone know how to fix this? I'm running Single User mode on Mac OSX 10.6.8.