Is there a mirror URL to download latest packages for Tumbleweed? We have a private network that cannot be connected to the Internet.
Hi and welcome to the Forum 
That’s a big ask since every Tumbleweed update is a new release and download, no ‘latest’ packages like the Leap releases (with an update repo). There is an update repo for Tumbleweed but that is just for emergency package release like the libzypp update last week that was released this way.
https://mirrors.opensuse.org/list/tumbleweed.html
So for March so far there have been seven releases times nnGB, remember the repository contains a lot more packages than what is on the DVD… A quick look shows just the x86_64 directory contains 21,000 packages