I found this forum looking for a new light tunnel for my InFocus X3. After seeing Sheridan give the dreaded information that InFocus had discontinued selling parts for these projectors, I figured I may as well give some options a try before I threw it in the trash.
I ended up going out in my garage and found a piece of polished stainless steel that you can purchase in the form of an exhaust band clamp. I measured the dimensions for my light tunnel and scribed marks on the stainless to mark my cutting points (I used 2 factory edges and only made 2 cuts) and also my "folding" points. After cutting the piece of stainless to size, I verified the length was PERFECT; if it's too long, it will tweek the "diffuser" by the color wheel towards the color wheel. I then took a pair of narrow long nose (needle nose) pliers with no serrations (smooth inside) and used them as a metal brake. I made the center bend first then made the 2 outer bends to form the tunnel. Then tweeked it to make sure that it was completely square with no twist in the tunnel. I installed it in place of my collapsed tunnel and reassembled. Fired up the projector and VOILA! great picture with no more brown spots!!!
Key thing to keep in mind is you want to get a metal as reflective as possible to keep the picture bright. I have kicked around using a piece of chrome plated metal to make another one. If you use a piece that is chromed, you will have to verify that the chrome did not start to flake after you bent the piece of metal.
If need be, I can post up some pics and build another to make a step by step on building your own light tunnel to save your InFocus projector from the landfill.