If you're in chroot then wget has not yet been installed.
If it was me I'd use wget from the host system to download
http://ftp.gnu.org/gnu/grub/grub-2.02.tar.xz and then mount
the system you are building and either copy or move the tar.xz
over to sources directory on the lfs system that is being
built. It's sometimes complicated I know if you are new.
Do you really need grub? I use the grub2 that is installed
on my host Ubuntu system to do the grub stuff. The lfs you
are building requires only a kernel in /boot. I run "update-grub"
from my host system and it sees and picks up the lfs system
and adds it to the grub boot menu. You need grub only on
one system to boot any other systems on your disks.
Just a thought for you to consider.