hi
this demo was created with the professional-edition of gamestudio. in this edition the author have the feature to pack all content (scripts, models, levels, ...) in a encrypted wrs-file.
the only way to get the sourcecode is, that you contact the author of the game (take a look in the readme-file). but you should know: packing the content in a wrs-file is a way to protect the sources of the game. and if the author uses this feature, it is improbably that the author will give it to you, otherwise he wouldnt do that