In addition to interviews in collected works or journals that VCU holds, many author interviews can be found online. Here are a few possible sources.
Though VCU Libraries does have a number of books concerning writing genre fiction, some are not classed under "Fiction -- Authorship." Searches for "mystery and authorship," "fantasy and interviews," or similar combinations will return some relevant books, although genre terms will often bring up items with the word involved that have nothing to do with the genre. Once you have found a relevant book, examine the subject headings and click on them to get similar books.