First of all, please uninstall, or at least disable, the epel repo. ClearOS already comes with the clearos-epel repo which is disabled by default. However it is already configured to exclude packages which are known to break ClearOS. You can enable the repo for specific installations using the --enablerepo=clearos-epel with your yum command. Also I suggest, if you are a newbie, not to run yum with the "-y" switch. It is much safer to see what yum is going to do then hit the "y" key if you're happy.

Then have a quick hunt for zabbix:

yum list zabbix* --enablerepo=* --showduplicates

This will give you an idea of which ClearOS repos contain the package, then go for the safer repos first. If you can't find it, you'll need to hunt down the rpm's from the wider internet with your favourite search engine.