How about totally fictional Australian Marine Corps markings. What ever that would be. Maybe a Kangaroo with globe and anchor?
For many years there has been an ongoing debate about the reorganisation of the Australian Army along the lines of the USMC's "expeditionary force". This has caused some wags to call it the "Royal Australian Army Marine Corps". I did a RAMC (Royal Australian Marine Corps) V-22 sometime ago. As to a badge, I suspect it would be a variation on either the RAN's:
Or the Army's Rising Sun:
Perhaps with as you mention, a globe and anchor, in the background. Perhaps apophenia or someone else might like to have a go?