Searching on Google, it appears that there is no official redirector currently.
mirrors.ubuntu.com can be used as a redirector (sort-of), by using it in
/etc/apt/sources.list. For example, you can replace the following lines:
deb http://fr.archive.ubuntu.com/ubuntu/ xenial main restricted
deb-src http://fr.archive.ubuntu.com/ubuntu/ xenial main restricted
with these lines:
deb mirror://mirrors.ubuntu.com/mirrors.txt xenial main restricted
deb-src mirror://mirrors.ubuntu.com/mirrors.txt xenial main restricted
You can perform the change for all the lines that use a specific mirror (
fr.archive.ubuntu.com in my example). Do not perform the change for
http://security.ubuntu.com/ubuntu as it is important it remains as it is for urgent security releases (bypassing mirror delays).
/etc/apt/sources.list is an important file. Make a backup copy before you edit it. You need to edit it as root (or rather, edit a copy as a regular user, then put the edited copy back into
/etc/apt as root).
Note also that this
mirror method sometimes failed in recent Ubuntu releases. I may have been fixed in 16.04, but the bug is still open: https://bugs.launchpad.net/ubuntu/+source/apt/+bug/1479045