Linux Turnkey SNMP

Question

I'm running a Linux turnkey web server and I'm trying to get PHP functions such as, snmpget() to work on my server. It looks like I require a "apt-get install net-snmp" command to be run in order for me to use SNMP commands. but the server says "Unable to locate package net-snmp"

This is where I'm told I require Net-SNMP; http://php.net/manual/en/snmp.requirements.php

So I'm not sure how to install this?