I recently read this as part of the translator's preface of St. John's Homilies on the Beatitudes, and remembered your question about his diary, and thought that it may be of interest to you.
The Homilies also constitute a link between St. John's diaries, preserved in Russian archives—only a minuscule portion of which is contained in My Life in Christ—and his sermons.
So, apparently, his full diaries are available (perhaps, though, only in Russian). It goes on to suggest that the book could be read alongside the diaries for better clarification of St. John's thoughts, suggesting that this is perhaps available publicly.
Hope this helps!