“Can’t somebody bring me a one-handed economist?” — Walter W. Heller’s account, as printed in Edwin Nourse’s New York Times obituary of 10 April 1974. This is the earliest attribution to Truman that Quote Investigator has found ↗.
“John, do you think you could find me a one-armed economist?” — what John R. Steelman, Truman’s Assistant to the President, recalled in a 1986 telephone conversation with Truman Library staff, as relayed by archivist Randy Sowell in 2019 ↗. Same scene, different limb.
“Get me a one-handed economist! All my economists say, ‘on the one hand, . . . but on the other.’” — as printed in Paul F. Boller’s Presidential Anecdotes (1996), where the supporting citation is an indirect one from 1980 ↗.
“Give me a one-handed economist!” — the form that actually circulates on the quote aggregators, where Goodreads, AZQuotes and Quotefancy all print it as a flat Truman quotation with no citation of any kind. It is Boller’s sentence with the verb changed, one step further from a source that was already indirect.