The package for OS X 10.6 can be found here:
http://www.dynare.org/download/dynare-4.2/mac-os-xWe will try to make a package for 10.5 sometime next week, though we will definitely be dropping support for 10.5 for the Dynare 4.3 release (and Dynare 4.2.2 if there is one).
In general, you can expect the OS X packages to come out up to several weeks after the Windows release because we don't develop on Macs and have to update software and go through the build process in addition to our regular activities.