Liability covereage should be easy to get and most independent tradespersons out there probably have it. It shouldn't be hard to find a local agent that can set you up. You can email me to get our agent's name. And the policy should cover you wherever you work; I'm not as sure about this but ask the agent. It shouldn't be as mysterious as Worker's Comp.
I also think that any liability policy would cover multiple trades, whatever your business is. Again, Worker's Comp is more complicated, I believe. Just tell the agent what you do and want covered and let them do the legwork to find a provider.