Fink makes pre-compiled versions of its "stable" packages available for automatic installation (when the package license permits). Many of these packages were released under the Gnu Public License (GPL), and the Fink project takes its obligations under the GPL quite seriously.
The Fink Archive Brower, at http://bindist.finkmirrors.net/bindist/dists/, allows the user to obtain any of these packages, or the corresponding source files, patches, and build instructions. Each "distribution" within the archive (which is specific to a particular version of OS X) is divided into "crypto" and "main" sections, each of which is further subdivided. The binary-darwin-architecture directories contain the actual binaries, again further subdivided by topic. The finkinfo directories contain the corresponding files with build instructions, as well as patch files, and the source directories contain the source files. (Actually, the way this is implemented, they contain symbolic links to the Distfiles copy of the source files).
In this way, knowing the package name, a user can obtain not only the source file, but all necessary patch files and build instructions that were used in creating the binary version. The build instructions are carefully documented in the Fink Packaging Manual.