I agree the quality of Rob's CAI system is top notch, having one myself. If I understand what you are looking for you could use 3.5 >3" silicone couplers. You'll be making some work for yourself. Part of what Rob provides is the experience and testing of his products. For couplers I have used Verociousmotorsports.com
If you mean the piece that attaches to the throttle body you will not likely find anything that has curves to direct the incoming air but a "T" with the air hitting itself right before the TB, not really a good thing. I know as I looked for something when I got my car and did not want to spend the money on the NW system but then I went with it and am pleased I did.