There is no software-versioning-system-based repository for this viewer (well there is, but just a "manual" one), because I, Henri Beauchamp (SL and OpenSim grids avatar name), is the one and only maintainer for it and I find git, mercurial, svn, cvs & Co way too cumbersome and heavy to use when developing alone; I'm a Nedit, xterm+bash, diff, patch, grep, find, and sed guy, and can develop blazingly fast with just these few (totally antediluvian, but nonetheless lovely) tools, when git & Co would just slow me down and make me pester like the old fart I am. :-P
However, you will find on this site every file needed to rebuild the viewer (and its third parties libraries) from sources (1), as well as the full backward history of the viewer sources (2) for each released build, in the form of incremental diff files. This is in strict conformance with the GPL v2 under which this viewer is licensed.
So... Here are the links to the various sources and components making up the Cool VL Viewer "repository":
Main sources for the current releases.
Incremental diffs to reconstitute the sources of previous releases (read the text at the bottom of that page to learn how to reconstitue any viewer build sources from them).
Third party libraries used to build the current releases (when not the ones used for building LL's official viewer, or possibly (3), another TPV viewer: see install.xml in the viewer sources tree for links to the latter; you may also use the ./scripts/get-prebuilt-packages.sh script in the viewer sources tree to fetch the corresponding pre-built packages based on their type or provider).
Third party libraries sources and/or build scripts (when not the ones used for building LL's official viewer, or possibly, another TPV viewer (3): see Linden Lab's github for the sources of LL's third party libraries, or any other TPV's repository for their own libraries).
To learn how build the viewer by yourself from the above sources, please do read the detailed instructions and prerequisites provided in the viewer sources tree linden/doc/ sub-directory. In case of any difficulty related to a missing build component or unclear build instructions, please do report and ask for help on the appropriate forum.
(1) And unlike LL's viewer build system, mine is self-contained: every build script is part of the sources tree, and building the viewer typically consists in launching a single shell/batch script from a terminal.
(2) But not for third party libraries: those are the responsibility of their respective authors/maintainers, not mine...
(3) A rare occurrence (since I would most likely rebuild the corresponding libraries myself). Not currently (2022-11-20) used.