Back in the day, Polycount was the place Modelers gathered to discuss and share models.  As a result is was a treasure trove of models for Q3 mappers to utilize.  Sometime in 2006 the site changed and eventually the q3 community-driven content has seemed to all but vanish.  However, I stumbled across the IOQuake3 site again.  And much to my pleasant suprise I found a dump of the old Polycount Q3 character models!

And here's an archived page detailing how to create models for Quake 3 Arena.