I don't know of a pre-packaged solution, sorry...
... but couldn't you just a little script that connected to the database and saved all the stored procedures to disk as text files? Then the script would add all the text files to the SVN repository by making a system call to 'svn add'.
Then you'd probably want another script to connect to the DB, drop all stored procedures and load all the repository stored procedures from disk. This script would need to be run each time you ran "svn up" and had new/changed stored procedures.
I'm not sure if this can be accomplished with MS SQL, but I'm fairly confident that MySQL would accommodate this. If writing SVN extensions to do this is too complicated, Capistrano supports checkin/checkout scripts, IIRC.