I have been searching for X308 replacement exhaust systems on the Net since yesterday and I do not seem to be able to find any. There are some performance exhaust systems available, though. Even Rockauto has nothing available.

Is it really this bad situation if one would like to have a stock replacement system?

 

I would email them on this before ordering anything to be sure everything is there you need... https://www.carid.com/2000-jaguar-xj...-exhaust-kits/
...because the mufflers (silencers) alone are around $350 ea (US) if you want original.
I'm quite sure Borla made these originally. But another performance option would be Paramount... https://www.paramount-performance.co...st-System.html ...I'm sure they would work with you if you want it more subtle. They are in the UK.