Having had Seattle in 1962, Spokane in 1974 and Vancouver, B.C., in 1986, the Pacific Northwest certainly had more than its share of world's fairs in those decades. But there was briefly some serious consideration to a fair in 1989 in Tacoma, Wash., to make the 100th anniversary of Washington's statehood. In fact, the state Legislature even authorized a commission to study the idea. But it obviously never led to an event.
I also remember reading that there was apparently some kind of planning that took place for a fair in 1976 in Philadelphia, the year of our Bicentennial. But that also went nowhere.
I also read one time that, either in the 60s or 70s, there was some discussion about a fair somewhere in the Los Angeles area -- I think perhaps it was proposed for nearby Corona. But that's all I know about it.