I had the exact same discussion on the Go forums a while back and the conclusion was basically the same...roll your own maps with RW locks:
https://groups.google.com/forum/?fromgroups#!searchin/golang-nuts/furmankiewicz/golang-nuts/jjjvXG4HdUw/ffWytKQ7X9YJBut...at the end someone actually built lock-free data structures in Go out of this:
https://github.com/zond/gotomic