Aye, the dungeons are never limited to the group finder only thankfully. And infact I extremely highly recommend you don't do them that way.
The correct, and recommended way to do the group dungeons is via the Undaunted guild:
- In each major city (generally the first one you reach, or sometimes the 2nd, youll know due to it's size and the fact it has a bank) - search out the local tavern. Inside you'll find 3 undaunted members (at least):
- 1 will tell you the location of the local campaigns dungeon, and mark it on your map
- 1 will tell you the 2 locations of hte other campaigns dungeons, and mark them on your map too.
- The last will just be a drunk that wants a drink. You can purchase him one, and it will count towards an achievement. (which grants undaunted points)
So yea, you can do them at anytime, at any level, with any party thankfully. Just talk to those guys, then open up your map and port in. Battle on.