Where can I find clinical trial data published in JAMA?
Online repository

Today, most journals (although t may depend on the field) require author to upload their data. The paper you are interested in was published in 1967 (internet was invented in 1969). It is very likely that the data have not been uploaded. It is also possible that the data have never been compiled numerically but is only on paper.

Ask the authors

Your best chance is to contact the authors directly and politely ask if they can give you their data. The author might be hard to contact as well as they may have changed university, be retired or even dead.

Possible loss of data

If you can contact the authors, then it is not unlikely that the data have just been lost. The loss might be due to a flood, to a technical issue or just because they don't know where it was placed.