4x4 exhausts are an issue it seems here's
@WitleyPanda thread (for example, there are a couple of others on here)
https://www.fiatforum.com/threads/4x4-1-3mj-exhaust.518397/ - use the search function which is pretty good.
I think the issue is there was never a sufficient production volume of the 4x4 to interest pattern part manufacturers. My 63 plate one has limited life expectancy now...