Let's use a Wix example site (not a client, just a sample from their page) as my example. Say you wanted to check:
http://www.kingskolacheny.com/#!press/crr2
In the source code I see the escaped fragment URL. This is the one you can find a cache for:
http://www.kingskolacheny.com/?escaped_fragment=press/crr2
That leads me to: http://webcache.googleusercontent.com/search?q=cache:http://www.kingskolacheny.com/?escaped_fragment=press/crr2
If your #! URLs are not setup this way, you will struggle to see it. One page websites are ... one page. But if you have escaped fragment URLs setup, you should be able to submit those and go from there.
The easiest way I know to find these is Screaming Frog, Ajax tab, Ugly URL field - try that one.