A few tips:
Take a tour of the traders in big centres. Check which guilds have the traders, how many items they have for sale and if they keep the trader over a few weeks. When you find one you like, you can look ask in Zone if anyone from that guild is on or send a message to one of the sellers.
Usually, anyone from a trading guild can invite new members. Whenever I see someone in zone asking to join a guild, I check if the trading guild I'm part of has a spot and if they do I whisper the person and offer to add them.
I am on NA though, so I can't help you unfortunately.