I know there is a list on Wikipedia of the books in the "Matador series", but I'm primarily interested in the society/pseudo-religion "The Siblings of the Shroud" explored mainly in "The 97th Step". Has this group appeared as anything more than cameos in any of his other books?
Siblings of the Shroud are mostly in The 97th Step. They are also in The Man Who Never Missed but less prominently.
Eventually there will be a novel entitled "The Siblings of the Shroud".