Q: Is it possible to sync together more gameboys by
using a 4 way link cable and setting one gameboy to master and then
the rest to slave?
A: The 4-way cable doesn't work. But it's possible to sync multiple Game Boys by splitting and splicing regular Game Link? cables.
This is a 6-way LSDJ or nanoloop sync-box i made :

Q: Who made this 6-way LSDJ/Nanoloop sync box and what can I do to purchase one?
A: Was made by Delfy
http://www.myspace.com/delfycreations
Q: Is there a tutorial available for one who knows nothing about splicing gameboy link cables or any cable in general? If not, can anyone make one?