One solution could be to find the address by looking into
Bottom Of home page (some sites put their address at footer)
Find address from following pages linked to the main page Contact Us, About Us
None of the above approach is guaranteed to retrieve an address ...but is one step closer.
Next option could be to lookup the whois to find the registered address. If you are a paid user of lookup service you may be able to lookup address for a particular registrar. But then, there are registries that keeps the address hidden (my own website has the address hidden, it shows the address of service provider).... so not always a success.
You can also lookup other services like Crunchbase, and any other directory service as a fallback.
So , let's say we assume you are able to get address of 60-70% websites with all techniques mentioned above. There are situation, where you will end up getting multiple address. You should have a logic to resolve to a particular address. Just think of getting address of Pizza Hut from pizzahut.com :-)
You can add more intelligence...but hope this is good enough to get you started on right direction.