I know how you feel especially in regards to walkups and continuity. As you said, sometimes a character just doesn't have a reason to speak to another one. I think everyone gave really great and sound advice, but one thing that sometimes helps me is to look for a reason why my character may speak to someone. Perhaps they have a really intriguing outfit, my character might comment on that and then I just see where the conversation goes. You never know! If the character itself is shy, you might even be able to message the person you have interest in RPing with and working out something OOC with their character. As far as I've seen most people are very happy to get a tell or a message and would be happy to work something out!
Celye Cimeaurant ~ Kana Tsuwamono ~ U'kijah Fijh ~ Cynnie Thorneweald