Welcome,
The forum at http://www.4xlab.net/cs/forums/16/ShowForum.aspx is open to all registered users and provides more than enough source code from indicators to complete trading systems to start doing practical experiments with Forex mechanical trading systems.
The forum at http://www.4xlab.net/cs/forums/6/ShowForum.aspx provides the source for the simulation engine and is an invitation only forum. You gain access by making useful contributing to the forums here.
Thanks and welcome to the site.