You're not going to be able to get this from the ePO query engine, as ePO 4 does not know what the firewall is and so cannot query for it. You should be able to get it from the DB though, as the properties for the firewall should still be being reported. Try something like this:
select el.nodename from epoleafnode el join epoproductproperties ep on
ep.parentid = el.autoid
where ep.productcode like 'FIRE%'
Great, thanks for pointing me in the right direction. I guessed that this would be the only way.
SELECT EPOLeafNode.NodeName, EPOProductProperties.ProductCode, EPOProductProperties.LastInstalled, EPOProductProperties.InstalledPath,
FROM EPOLeafNode INNER JOIN
EPOProductProperties ON EPOLeafNode.AutoID = EPOProductProperties.ParentID INNER JOIN
EPOComputerProperties ON EPOLeafNode.AutoID = EPOComputerProperties.ParentID
WHERE (EPOProductProperties.ProductCode = N'FIREWALL8500')
That'll work, but will only show you the firewall 8.5 machines, of course - you'll need to modify it for your version 8 machines