Nobody makes what you're looking for 67 LS1. Nor does anyone make mandrel bent 2.25" either, which is a real shame. A 2-1/4" tailpipe is good for 400+hp, especially on a street car, and makes installation and fitment so much easier. It would meet the needs of 95% of the Chevelles out there. The only one that is producing kits with 2" exhaust is Gardner, and that's a complete (very high-end, very high quality) system. They will not sell just tailpipes. Also not mandrel bent, as that is not factory correct. I doubt there are many local shops out there with the ability to mandrel bend custom tailpipes. Please let us know if you find one.
Your thought process on using 2" exhaust is sound thinking though. IIRC, you have a V6. If that's correct, anything bigger than that only slows down exhaust velocity and adds noise.