Orvis makes a line that is designed to pair with a lightweight rod like the Superfine Trout Bum, called the Hydros Superfine. I actually have this line brand new, but I don;t own a 3 weight. If you decide this line sounds like it fits your needs shoot me a message. Its actually for sale on the Swap forum right now.
Besides the Orvis line, I would also agree that the Rio Selective Trout line is a great line. I use it on my go to 4 weight rod.