Yeah, but according to elfman, the guy says he retired a Master Chief Petty Officer. Guess I'm just not understanding the terms correctly.
There are over 3000 Master Chief Petty Officers (MCPO) CURRENTLY SERVING.
http://www.news.navy.mil/search/print.asp?story_id=6345&VIRIN=&imagetype=0&page=1
MACM is an MCPO in the law enforcement area (Master-At-Arms)
There are several other flavors of MCPOs. You can get some idea from this promotions list:
http://www.bupers.navy.mil/navadmin/nav03/nav03074.txt