M8-.80??
So, I took the exhaust clamp to my local auto parts store, where they tried selling me an M8-1.0, which is the finest thread size available (anywhere). That didn't work, and putting a special gauge on the thread, we discovered that the thread size is actually M8-.80 I spent about an hour scowering the internet for this size nut, with absolutely no luck. They simply don't make that size. So what I did was buy an M8-1.25 stainless bolt, cut off it's hex head, cut off the M8-.8 threads off the clamp, and TIG weld the new threads in its place.
Problem Solved!
For about $20, I could have bought another clamp assembly from ebay. However, I love welding and am too impatient to deal with delivery time.