P. Harvery-Smith has released an IRIX port of 3D Realm's Rise of the Triad based on the Linux open source port. Rise of the Triad requires the datafiles from either the full commercial release or optionally the demo (download links below).
Download the binaries, instructions and souce code from the official IRIX port site:
The shareware datafiles can be downloaded at:
The datafiles for the full version are available from Abandonware Games (registration required).
Finally, here's a link to a great article on ROTT which covers the history of the game among other things; it's an excellent read: