You can buy ZRGO4fun fares online. They are just hard to find.
First you need to find a city pair that the fare is offered between.
Second you need to read the fare rules to learn the days of travel and that you have a Saturday night stay (usually a minimum 6 day stay)
Third you need to ensure that there is Z availability on the days you want to travel.
You can use travelocity to check for the published fare & the fare rules. You can use the availability tool to check for Z availability. Then you can go to the NW web site and search for them.
It may just be easier to call NW and have them find everything for you. Why is buying them online important to you?
For example, Z fares are available from SFO->AMS both ZRGO4FUN and ZHGO4FUN. RT SFO->AMS is about $2400 per ticket. It wasn't much work at all to find available dates. Fares aren't dirt cheap but do get you RT in First & WBC and 150% EQM.
[This message has been edited by doglover (edited Feb 06, 2004).]