Here is Graham Nelson's Blorb page, including his "perlBlorb" tool for assembling Blorb files from individual graphics and sound files.
Here is blorbtool.py, a Python script for examining and manipulating Blorb files.
Here is Blorblib 1.0.2 (compressed tar file, 20K). This contains ANSI C source code for a library you can insert in a Z-code interpreter to read Blorb files. It also contains source for "blorbscan", a tool to read and analyze Blorb files. However, it has not been updated since Blorb 1.1; so its utility may be limited. See Graham's page (above) for more current Blorb tools.