What is the status of the PostQUEL source code? Recently as part of my answer to "Is the keyword “ALIAS” actually used?" I wanted to go back further than Postgres95. Postgres95 is the first version of Postgres that was migrated to use SQL rather than QUEL.

Is POSTQUEL (the version that used QUEL) open source and is it available anywhere? The PostgreSQL repo starts with an import of Postgres95.
The database was not known as POSTQUEL, but as POSTGRES. PostQUEL is "an incompatible, extended version of QUEL (the Ingres query language)."

As to the source code, I found it linked from this Command Prompt Blog Post, 

You can find it available on the POSTGRES Project page at Berkeley.