Fork of abandoned SVN mirror - how to keep up to date with the SVN

For some months, I have been working on a http://github.com/jamespetts/simutrans-experimental/tree fork of the popular open source transport simulation game, http://www.simutrans.com Simutrans . Simutrans uses SVN as its official VCS, but I have been using Git, by forking an http://github.com/aburch/simutrans/tree/master unofficial mirror of the Simutrans SVN on Github. That has made it extremely easy for me to merge in updates to the trunk code whilst continuing to work on my branch.

However, last week, the unofficial mirror on Github suddenly stopped tracking the updates on the SVN. I have sent a message to the person who administers it, but he has not been around for a long time, and I fear that he probably will not reply - he did not reply to a message that I sent him some time ago. I do not really know what to do now to keep my branch synchronised. I have tried creating my own mirror of the SVN on Github, but there are two problems: (1) I cannot for the life of me get the creation of the mirror to work - it gets stuck permanently at "fetching authors"; and (2) even if I did succeed in creating a mirror, it would no longer be the same as the branch from which I forked, so Git would not be able to keep a track of which parts of the code I intend to keep different from the trunk, and which are the new updates to the trunk that I want to incorporate in my branch.

What is the best way of dealing with this mess to try to re-instate an easy and reliable system of taking updates from the SVN and merging them into my branched code?