That tidbit was buried in a footnote on page 176 of the Justice Department's recently released 476-page Inspector General (IG) report on the FBI's Russia collusion investigation. Steele made the remarks about Buzzfeed and the McCain staff member during an interview with the IG.
The relevant footnote relates:
Steele testified in foreign litigation that he did not provide his reports to journalists or media organizations and did not authorize anyone to share them. According to the McCain Institute staff member's testimony in the same litigation, Steele requested that the staff member meet with BuzzFeed, and that Steele neither requested nor prohibited the staff member from sharing the reports with BuzzFeed. Additionally, the staff member testified that Steele was aware that the staff member was furnishing Steele's reports to The Washington Post.