The Oregon Department of Agriculture used to have a program where cinnabar moths could be obtained, but they no longer do so because the demand had dropped. The moths had an established population in the Willamette Valley. Now Tansy is rearing its ugly head again. Here is the ODAs information about Tansy Ragwort. The OSU Extension Weed Control Handbook has a section on controlling problems weeds. Here is a link to the Tansy Ragwort section. The Yamhill Soil and Water Conservation District also has a brochure, Managing Tansy Ragwort. All of these will help you in your efforts.
Another thought is that you might contact the ODA Noxious Weed Department and request that they reinstitute the cinnabar moth program. Good luck in your battle against tansy ragwort.