The original publisher, Softdisk sold many of its assets to Flat Rock Software in the 2000s. Flat Rock sold off bits and pieces over the years, and the Catacomb games were one of the last things it held [1]. In 2017, I wrote a toy implementation of Catacomb 3D in WebGL [2]. Since the project used art that was under copyright, I contacted Richard at Flat Rock to ask permission to use it. That conversation eventually led to me deciding to buy the overall game ownership from him [3].
[1]: https://web.archive.org/web/20150101022225/http://www.flatro...
[2]: https://github.com/jayschwa/CatacombWebGL
[3]: https://web.archive.org/web/20170623155041/http://www.flatro...