Instead of answering this question directly I will just tell you some ideas how that is done in ruby:
1) in a project root you have a one file, which has a list of libraries you would like to use with their version.
"popular lib1, version > 2.0" ,
"popular lib 2, version 1.55, store in www.aaa.bbb/1.55.tgz",
"popular lib 3, stored on www.xxx.com/1.git, any version"
2) the tool analyzes you version requirements and finds best version of libs (so all version requirements are matched).
so you have some sort of ./cache folder which contains copy of downloaded files.
So for a c# I would always copy whole libraries in the project root folder, like
libs3rdparty/ with name. I dont like any sort of shared libraries per whole companies, with such a cheep disk space there is no sense in that. As an option ( to make SVN size smaller) you could create an install.bat file which takes lib versions from certain places and adds the libs3rdparty to the svnignore.