Well why won't the "guys" who have rights to the source code, release it ?
I mean they don't have anything to lose. The game could just get new reputation in the gaming community.
I've asked this question in the past, but the response I got was basically that they didn't get the source in the liquidation of Headfirst. Your best bet is to either reverse engineer the existing game, and write new shaders that work, write a new engine from that -- or start over and figure out what are in the resource files, and build an engine that can work with said files.
Neither are very conventional ways to go about it, so you'd probably be better off going with recreating it. For this purpose, I think the id Tech 4.0 (Doom 3) engine would be a good candidate as its unified light and shadow architecture would allow you to create a very foreboding and creepy atmosphere for the game, and it's a very elegant and well-designed engine for the task. If you go this route with it, I think one of the steps you should consider taking is to reduce the first-person shooter elements, and intensify the amount of mechanics we see up until the point Jack gets the Crowbar. Maybe even combine those together, and have Jack gain the crowbar but only as a non-combat tool, and have the only occasions for mounted weaponry during important moments -- the best examples of this are the car ride during AotF, The Devil's Reef ship battle, and of course the exception is at the point of The Air-Filled Tunnels.