Steve, SPF does not supply any cats, any car with them was done post factory. There are some installers who have fabb'ed cats for UK and OZ builds as they are required on most builds there.
Last I heard was Frank Catt Wealden Engineering doing some, he had the cats fitted inside the silencers, which are good for keeping the noise down especially on tracks like Goodwood.
You're going to have to have the exhaust with cats custom fabricated. At one point I thought I might have to go that route for emissions testing. Short ones like this might work: