Where is the source code for the earliest C compilers?

It is not a query like "what tool can I use to execute ...?" Which is not related to stackoverflow.

In a few questions, the answers that seem to have some credentials relate to the analysis of the source code of early compilers, for example:

• Why was the switch statement designed to require a break? where he is mentioned in Sun ANSI C compiler front end
  
  Peter van der Linden.
• Is the "for (;;)" idiom for an infinite loop correctly assigned to the PDP-11 C compiler? where asked about for(;;)
  
  idiom wrt "early PDP-11" compiler
• The code for malloc and free belongs to modern implementationglibc
  
  

Also wikipedia describes several old compilers such as:

• https://en.wikipedia.org/wiki/Portable_C_Compiler by Steven C. Johnson from Bell Labs in the mid-seventies
• https://en.wikipedia.org/wiki/Amsterdam_Compiler_Kit by Andrew Tanenbaum in the early eighties (but certainly not open source, or we wouldn't have gcc
  
  )
• https://en.wikipedia.org/wiki/GNU_Compiler_Collection by Richard Stallman in 1987.

However, there are no links to the earliest versions that are of the greatest historical interest!

Given that the truth lies in the code , it would be great to know where to find the source code for the earliest C compilers.