Here is a list of authors who wrote books on Service Design that I found by searching on Goodreads and Google.
I've listed here only the authors who have written one or more books focused on service design and have that term in their book titles. I've put those authors in no particular order.
And myself, or Daniele Catalanotto
You can find more authors by looking at the lists of Service Design books on Goodreads or on servicedesignbooks.org