Portland: http://www.oregonregionsolo2.com
Eugene: http://www.eescc.org
Medford: http://www.ssccmedford.com
Salem: http://www.wmclub.org
There is also a club in Redmond, but there is no website.
Eugene did a great job of compiling all the Oregon club schedules. You can find it at their website.
Edit: Added Salem website.