Repositories

By default Devuan uses deb.devuan.org in /etc/apt/sources.list as explained here:
https://www.devuan.org/os/packages

That is not a repo in of itself, but attempts to hook you up to the best mirror(s) for your location.
Sometimes though, various issues usually related to DNS can keep it from working properly, there
are multiple threads on the Devuan forum about fixing the issues, just do a search.

An alternate workaround, is to change sources.list to directly use a mirror that works for you.
In Vuu-do and the other iso's based on Devuan 5 (daedalus), I have changed it to reflect the mirror
that works best for me here in the midwest US. So here is the sources .list that i'm currently using:

deb http://gnlug.org/pub/devuan/merged/ daedalus main contrib non-free non-free-firmware 

deb http://gnlug.org/pub/devuan/merged/ daedalus-updates main 

deb http://gnlug.org/pub/devuan/merged/ daedalus-security main

To look for mirrors close to you, check a couple of places:
https://www.devuan.org/get-devuan
http://deb.devuan.org/mirror_list.txt