Eliezer: I am unable to find online the referenced text of his 1930 attack on the mind as an "old wives' tale".

The text is Watson's book "Behaviorism", to which there is limited access on Google Books. The phrase occurs exactly once, on p.118, but not in close connection with the mind. However, searching the text for "mind" provides ample evidence that he claimed there was no such thing. A few examples:

"X. Talking and thinking. Which, when rightly understood, goes far in breaking down the fiction that there is any such thing as 'mental' life." (Table of contents)

"How do you suppose Patou builds a new gown? Has he any "picture in his mind" of what the gown is to look like when it is finished? He has not, or he would not waste his time making it up; he would make a rough sketch of it or he would tell his assistant how to make it." (p.198)

"If 'mind' acts on body, then all physical laws are invalid." (p.243, emphasis in the original)

The second quote is particularly interesting, because at that point Watson is face to face with the truth, then turns 180 degrees away from it. A picture in his mind of the finished gown is precisely what the dressmaker has. He intends to perceive a gown of such and such a form, and the actions he takes in making it are chosen to produce that perception. The actions stop when he sees before him the gown that he conceived.

The last quote suggests an explanation, if not a justification, for his position. He could not solve the question "what is mind?", and hit the Ignore button.