There's X World http://auc.edu.au/xworld/about/. Devworld looks interesting http://2016.devworld.com.au but seems more dev related than admin.
Overseas we have http://macadmins.psu.edu and http://www.macsysadmin.se/2016/Home.html
Anything along those lines that's more local (not that I'd complain if work sent me overseas again)?
Don't really know of any related to Mac sysadmins. X World was a surprise to me.
But a number of different conferences will have a decent amount of mac admins attending. Spoke to quite a lot at vForum last year.