How can I retrieve the remote git address of a repo?

When you want to show an URL of remote branches, try:

git remote -v

If you have the name of the remote, you will be able with git 2.7 (Q4 2015), to use the new git remote get-url command:

git remote get-url origin

(nice pendant of git remote set-url origin <newurl>)

See commit 96f78d3 (16 Sep 2015) by Ben Boeckel (mathstuf).
^{(Merged by Junio C Hamano -- gitster -- in commit e437cbd, 05 Oct 2015)}

remote: add get-url subcommand

Expanding insteadOf is a part of ls-remote --url and there is no way to expand pushInsteadOf as well.
Add a get-url subcommand to be able to query both as well as a way to get all configured urls.

-v. Shows URLs of remote repositories when listing your current remote connections. By default, listing remote repositories only shows you their shortnames (e.g. "origin"). Using the "-v" option, you will also see the remote's URLs in listings.

git remote -v