I also have same requirement. I'm using a custom report with node details and software revision which shows the PanOS version as of now.
To display in the summary page, i have added a custom Universal Device poller with SNMP id obtained from internet.
Lets wait for some expert to help us.
I did build a custom Palo Alto node details poller a while ago that returned the software version, if you go into Manage Pollers in settings, and then Thwack community pollers you should be able to find it to test.
I can't guarantee it works with the latest versions as we no longer have any Palo devices.
I've ran into the same issue. SolarWinds doesn't populate the OID 18.104.22.168.22.214.171.124.126.96.36.199.1 for PaloAlto devices but it does for Cisco. I've confirmed it is the exact same OID.
Does any one find the solution for the same? I am also having the same issue with Palo Alto Devices