It would be the same as `pacman -Ss base` plus `pacman -Ss base-devel`. Note "-Ssq" would probably be much more useful in this context.
And be sure you have done "pacman -Syu" first, or at the very least "pacman -Sy".Edit: my comment is probably not relevant if you made it up to this point of the install already - I assume you successfully installed other things like a bootloader. I suspect this is a networking issue. Can you ping the mirrors?
Don't forget that "sudo" essentially means "su do". If you can't get pacman functioning in your chroot, try using the "pacstrap" command (see beginner's guide) but use the argument "pacman" in place of "base" or "base-devel", then chroot. That will reinstall pacman for you.