Have you tried the 'file' command on various *nix systems (can download for Windows too)? It mightn't know this format but I think it will tell you if it finds compressed (zipped) data streams in common formats, which will be your first step since many files have some form of compression.

I'll also echo the other comment about reverse engineering the reading functions. Some formats only include certain structures if necessary so even if you have a lot of files you might be missing some example data to complete the picture.