Is this info available for other airlines or ex locations? And the rules?
I assume you need to book a xonex at the earliest one year before the last flight of your itinerary?
Base fares used to be available on the oneworld website (and someone made a look up excel spreadsheet that pulled data from that site for easy reference), but the info was pulled a few years ago due to many markets requiring all in pricing and there is no way to know what the total taxes/surcharges will be without knowing class, route, airline and stops.
Now the only way to get base fares are to use a site like expert flyer, somehow get the tool to give you what you want and price the trip, or ask an agent.
links to the rules for oneworld RTW products are in the information section of the product page on the oneworld website (they are also available in expert flyer).
all oneworld members should have the same pricing for each departure point, but some airlines update prices more slowly then others should there be price changes.
You can book an xonex when the first flight/s (up to the first intercontinental flight) becomes available for booking in the ticketing airlines booking system (330-355 days out depending on airline). The last flight needs to be within 365 days of the first flight. This means it is possible to have the last flight almost 2 years after booking date. However, airlines prefer (and the online booking tool requires) that each flight be booked with a date rather then open dated as the rules allow (flights after first intercontinental departure may be open dated), so in practice, most people book once the last flight in available for booking.
An option is to put in dummy dates for any flights that are outside the booking period, maintaining time for planned connections/stopovers, then change the flight dates as the booking for the date you want become available (date/time/carrier changes are free, routing changes are $125US per change + any tax changes. Changing a connection to a stopover is a routing change.)