As I play through I've noticed that some of my toons stumble across them fairly frquently while others almost never. Does anyone have any tips, secrets are even general impressions about the best way to mine for story lines? Can any contact potentially have them, or is it only certain ones?
Uncle Yuan is one of those who seems to rarely get story lines, and he's a tough enough soloer as it is without having to endure nothing but a series of random encounters.
It's possible you have old storyarcs open. You can only have two non-zone (Hollows, Faultline, &c.) story arcs active at the same time. If that's the case, you need to go back and complete the old arcs before you can get any new ones. You can check this by looking in your contacts menu; if there's a little book beside the contact's name, you have a storyarc open for them. This is a huge pain and resulted in my level 50 blaster doing an entire arc of level 23 Sky Raiders at one point.
NoFuture has a pretty complete listing of all the storyarcs here (http://coh.nofuture.org.uk/story_arcs/) if you want more info.
Huh. That is the problem with Uncle Yuan - he has two arcs open. Gratzi.
Note also that most contacts have at least one story arc- some have two. They're pretty easy to find, if you don't have two arcs open already. I'd also, in general, recomend against having three active missions most of the time- there are times when you really need at least one open "mission slot", for example, when you need to do a mission to gain access to a store.