Hi Kelv,
Sorry to hear you've been visited by some Oic, who's unceremoniously purloined your cat, hope the damage isn't too bad.
I can recall a post I stumbled across a few months ago about cat options, so I sure some of our learned posters will soon be along to point you in the right direction.
Depending on damage, perhaps you might be able to get away with new cat, and some sections of exhaust tuning that you might have to fabricate repairs to the ends of either side, just had a quick look and eBay looks a possible source
https://www.ebay.co.uk/str/myriadexhaust
Let us know how you get on, and best of luck.
Cheers
Steve