Who's Who - by Reed Elsevier. I've heard, but not checked for myself, that it lists one "V. Plame" as his wife, in all editions from 1999 to 2003.
Check your local library for a copy. Most libraries have them dating back several years. Wilson is listed, suprisingly enough, under "Wilson."
Once it was determined that Wilson's wife suggested the mission, she could be identified as "Valerie Plame" by reading her husband's entry in "Who's Who in America." Link
Thanks for the other link too.