Check the Cascade ride sites at
www.cascade.org. There's the High Pass Challenge in mid-September (114 miles up to Windy Ridge); the Kitsap Fall Classic (not sure that's the right name), and then a bunch of daily rides w/small groups.
In January every year, there is an 8 or 10-ride series called the Winter Training Series that is co-sponsored by Cascade and the Seattle International Randonneurs. That's a great series -- every Saturday, rain or shine, rides start at around 40 miles and work their way up to a full century right before the Chilly Chilly weekend.