This was a known casualty of the Github migration. While not desirable, it was deemed an acceptable cost at the time.
Is there a reason these links can't be restored? It was very convenient to have them for navigating and understanding the history of the codebase.
Unlike Bzr, git doesn't have any notion of "foreign" revision identifiers. There's no index of SVN revision to Git revision in the git repository, so online tools don't support them. In order to have things like ticket-closing work, we moved Trac to point at Git as its primary repository, which disabled all these links as a consequence of its implementation.
However, if you are interested in spelunking to find the git hash of the ID, a hacky workaround is to go into your local repo and do 'git log --grep trunk@NNNNN' which will bring up the revision in question, because it'll hit the git-svn-id in the commit message. For example, `git log --grep 'trunk@33400' --pretty='%H'` reveals that the git revision for the commit you're asking about is 44e02d59d00926a34820f53a0b0ae78658844555.
I have no idea how to convince Trac that  is a valid revision link again; the fact that it doesn't has something to do with the svn->git configuration switch. If we could do that though, we could bring up a trivial Klein app to do the historical SVN revision mapping, by shelling out to that git command and redirecting to github.
Good to see you around again :-). Hope that helps!