I tried it via the party finder, world chat and discord, but got no response anywhere... is there some other way that I'm missing?

you don't... nodewars are a guild activity.

you either join a nodewar guild or make your current  guild start joining nodewars

alternatively you can merc (war hero) but people usually only take those they know

This is a good question. So if you are not in a node war guild and want to do node wars, you would need to become a mercenary (war hero) for another guild (most people call this merc'ing out). This temporarily puts you in another guild until after node wars. When the merc time is over, you will automatically be put back in your guild. Essentially you are paid for becoming a merc, and you receive the same rewards as the guild does after your merc period is over. 

There is no easy way to merc though merc'ing should work like the party finder. Right now you would need to join discord that allow you to put a message out that you are looking for a fight, or you can put in world chat that you are looking for a fight and want to become a merc.

Hope this helps