Free VerilogA simulators
The GPL spice simulator Ngspice has an extension called ADMS that compiles Verilog-AMS code into C code that works with the API used by spice simulators. So you'd end up with something that could be compiled into an executable that a spice simulator (like Ngspice) could simulate. 

Since Verilog-A is apparently just a subset of Verilog-AMS, this may suit your needs.