Hi,
Do you have a ProxySG with a WebFilter or Intelligence Services subscription? If so, you can also test URLs via your Proxy's test method:
hxxps://proxy.ip:port/ContentFilter/TestUrl/<URL pattern>
However, in the ProxySG URL requires authentication and unless scripted, can only categorize one URL at a time. The other alternative is that you can contact your Symantec Sales Engineer and ask if access to ThreatExplorer is possible.
Hope that helps.