There is no such version of tools.
In general, you cannot use the older versions of the server management tools on newer OS X software versions, and the server administrative tools associated with a particular release don't work across a particularly wide span of versions; typically with the current release, and the last few updates of the previous release.
To manage older releases of OS X Server, you will need to use an older OS X client system with older OS X Server management tools installed, or you will need to use Screen Sharing and the Server Admin and related tools that are already present within the target OS X Server system.
AFAIK, OS X Mountain Lion 10.8 doesn't have a download of the adminstration tools, you use the tools provided with the OS X Server download itself. The Workgroup Manager stuff allowed that to be added to the Mountain Lion Server environments. AFAIK, the Mountain Lion Server server adminstration tools cannot manage OS X Server 10.6; 10.7 is the last version that can, short of using Screen Sharing. (I'm running OS X 10.7 client and not 10.8 specifically because I have some old 10.6 servers that I'm still dealing with.)
Apple doesn't generally keep the older versions around for all that long (current and previous versions, in general), and the expectation is the older servers will either get upgraded, or will get replaced.