Since the "Getting started" link here is broken, and neither the word "download" nor "install" appear here or here, and this 1996 paper about "this new computer simulation code METADISE" doesn't mention anything about the code's availability, I think it's fair to assume that this code is not available for anyone from the public to download it.
This tutorial which appears to be for students at the University of Bath tells students to begin by following this instruction:
"Copy all source files of latest version from Aragonite/data2/Steve"
which suggests that even for people doing a class about METADISE, the only way (or at least, the easiest way) to obtain the software was to copy it directly from Steve Parker's folder, which would require you to have access to a very specific computer.
I agree with the suggestion by Tyberius which was to contact the author directly. Since you did that multiple times already, you might want to see if other people who claim to have used the software (for example, the authors of this paper can shed light on how they obtained it!