As an update, there is a "free" simulator being developed as a Gnu project, led by Al Davis,
called GnuCap.. and he is moving it to use verilog-AMS as its NATIVE netlisting language..
the developement version has significant verilog-A support already.
While it will run on a PC - it should probably be running Linux.. but you might be able to run it on OS-X
http://www.gnucap.org