For journals, contact the main editor and/or the editing board. This information is often on the journal's website.
For books, contact the editors or an agent.
Here is some sample text you can use in your email when contacting publishers.
Dear Dr. XXXXX,
On behalf of the Colgate University Promotion and Tenure Committee, I am requesting certain data pertaining to the journal “XXXXXXX" for use in a tenure review.
The specific data sought include:
Would you be so kind as to forward my request to the appropriate editor?
The data will be used only once in a confidential tenure review.
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