Cannot re-install synaptic on Buster.

Hi,

For reasons unknown to me, synaptic uninstalled itself about three weeks ago. I am using Buster on the desktop, with MATE as my desktop environment.

When i open up a terminal and try to re-install it, i get the following-

# apt update
Hit:1 http://ftp.us.debian.org/debian buster InRelease
Hit:2 http://ftp.us.debian.org/debian buster-updates InRelease
Hit:3 http://security.debian.org/debian-security buster/updates InRelease
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.

# apt install synaptic
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package synaptic is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'synaptic' has no installation candidate

/etc/apt/sources.list is the following-

deb http://ftp.us.debian.org/debian/ buster main contrib non-free
deb-src http://ftp.us.debian.org/debian/ buster main contrib non-free

deb http://ftp.us.debian.org/debian/ buster-updates main contrib non-free
deb-src http://ftp.us.debian.org/debian/ buster-updates main contrib non-free

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

I like using a GUI frontend to apt, and if anyone can help me get it back on my system i'd really appreciate it.

Thank you in advance for any help that may be provided.

- Kieran