Almost all of the BSD releases have been well preserved. If you want to find 1BSD, or 2BSD or 4.3-TAHOE BSD you can find them online with little fuss. However, if you search for 2.11BSD, you'll find it easily enough, but it won't be the original. You'll find either the latest patched version (2.11BSD pl 469), or one of the earlier popular version (pl 430 is popular). You can even find the RetroBSD project which used 2.11BSD as a starting point to create systems for tiny mips-based PIC controllers. You'll find every single patch that's been issued for the system.
The goal of the project is to create two main artifacts. First, it would be cool to have a git repo that has all the 2.11BSD patch points in it. Second, it would be really cool to have a near copy of the 2.11BSD release tapes. This project aims to create these artifacts in a reproducible way.