NOTE: WGP modules are NOT complete games. You must own the board game for them to be useful to you, as they are without rules, charts, etc. Support the developers, buy the game.
You can usually find copies of games for sale on E-Bay, or check out the following sources:
Fine
Games, a Portland based mail-order game retailer.
Boulder Games
European customers may be interested in checking out Leisure Games
of London
Currently the following modules are available for version 4: