The Oracle Certified Master, Java SE 6 Developer certification retires on November 30, 2016. You can purchase and download the Java SE 6 Developer Certified Master Assignment 1Z0-855 through this date. You have 6 months to complete and return the assignment and complete the Java SE 6 Developer Certified Master Essay 1Z0-856. Assignments and essays will be accepted through May 30, 2017. All grades should be provided by June 30, 2017. If you fail to pass the assignment on the first try, you will have thirty days to resubmit the assignment by completing and submitting Java SE 6 Developer Certified Master Assignment for Resubmission 1Z0-857 by July 30, 2017.
This certification path requires training to complete the path and earn certification. Candidates who have passed all exams and have not yet submitted the course form will have until December 30, 2017 to complete relevant training and submit the course form. After that date, this certification will no longer be granted.
Exam 1Z0-817: Upgrade OCP Java 6, 7 and 8 to Java SE 11 Developer Study Guide and Quiz
...and of course, I found the answer on the Oracle forum (in case anyone else was wondering):
"At this time, there is no plan to release a new version of the certification. Through careful job task analysis with the Java SE 8 certification release, it was determined that the OCM Developer role was no longer appropriate to keep as a separate certification and the that skills of that role should be included in the Programmer certifications."
From my point of view, it's a little disappointing, but it is what it is.