There exist quite a few legacy fonts, from the time that 8-bit-style encodings was the norm. Nowdays, most (if not all) spoken and ancient scripts have been added to the Unicode standard.
Therefore, if you have a legacy font, you can convert to Unicode using a guide by William J Poser. The guide uses Linear B as an example.
The program mentioned in the guide is pfaedit, which is now known as FontForge. FontForge is available in your Ubuntu distribution; simply search using the package manager.
Once you have a Unicode font, the next step is to prepare an input method so that you can write in this script. But that’s another blog post.