http://www.idsoftware.com/business/techdownloads/
Source code doesn't imply that they have released all the maps with it. The source code is for the engine(s) which is outdated compared to today's Doom 3, and Source engines.
It's mainly for modders and independent gave developers who want to intergrate a pre-made engine into their game to eliminate the need to create an engine.
Several stand-alone games which use one of the Quake engines have already been made. Check out Warsow (
http://www.warsow.net/), it's semi-popular with the old school Q3 players.
My advice to bob is to either buy the collector's edition and have it for sentimental gamer value or I can pick up Q1 at a local game store (assuming no one has bought it) 10 minutes away and ship it to you for free.