How to add package sources?

[Steve Litt <slitt@troubleshooters.com>]

Hi all,

I'm trying to install install flashplugin-nonfree on Wheezy 64 bit on
a dual core AMD, and it's been failing continuously. The error message
is something to the effect that it can't reach mirrors.rit.edu, and in
fact I cannot ping rit.edu, and when I traceroute to rit.edu it gets as
far as:

vl-5.car2.Buffalo1.Level3.net (4.69.141.146)  262.192 ms  261.916 ms
262.110 ms

and then gives me all stars out to the max 30 hops.

So I'm temporarily assuming the root cause is outside anything on my
LAN or cable modem. The following is my current /etc/apt/sources.list.

==========================================================
# 

# deb cdrom:[Debian GNU/Linux 7.5.0 _Wheezy_ - Official amd64 NETINST
Binary-1 20140426-13:35]/ wheezy main

deb http://mirror.rit.edu/debian/ wheezy main non-free contrib
deb-src http://mirror.rit.edu/debian/ wheezy main non-free contrib

deb http://security.debian.org/ wheezy/updates main contrib non-free
deb-src http://security.debian.org/ wheezy/updates main contrib non-free

# wheezy-updates, previously known as 'volatile'
deb http://mirror.rit.edu/debian/ wheezy-updates main contrib non-free
deb-src http://mirror.rit.edu/debian/ wheezy-updates main contrib
non-free

# ADDED BY SLITT FOR DOVECOT
deb http://www.backports.org/debian stable dovecot
deb-src http://www.backports.org/debian stable dovecot
==========================================================


Therefore I would assume I need to add another mirror to
my /etc/apt/sources.list. How would I find such mirrors? Do I just put
them below my corresponding rit.edu entries? Can I leave the rit.edu
entries intact? Until today, rit.edu has served me admirably. Is there
some sort of command I should run to add a mirror set, or do I just
edit sources.list?

Thanks,

SteveT

Steve Litt                *  http://www.troubleshooters.com/
Troubleshooting Training  *  Human Performance