The source is available on Github (in the repo jward212 just said), and the executable you probably are already using - it's the main download, available on the homepage as always. 

By the way, you'll probably be better off modifying and compiling the c++ source; porting GEL's update function to Lua would probably be a bit tricky, and might lag some, since Lua is slower than c++. 

EDIT: Looking at the source, it actually doesn't look too complicated, so good luck!