Bush, Lagoon, Fort Casey, all the suspected places, pretty much the same deal as the coho, minus the fish. As I understand it, the blush is kind of off the rose on this one. I think the glory days were back when the massive hatchery runs were going into the Skagit. People do still catch fish though. Dec-Jan I think, though now you'd probably do well to check it out a little later too for the natives (if it's open).
I don't know about patterns, but the gear guys use hootchies in pink, orange, chartreuse, so I would think big marabous would probably work, or other prawn/squid patterns. The bait-casters use a lot of lead to get down, so you might want a sinking line (even a little lead on the fly) and try an erratic, jigging retrieve.