I could only find a couple of suppliers with middle silencers on Ebay. Other suppliers appear to have no stock, but it doesn't mean they can't obtain them.
https://www.ebay.co.uk/itm/325602535848 ... p_homepage
https://www.ebay.co.uk/itm/185206281628 ... p_homepage
Same supplier, no delivery.
https://www.onlineautomotive.co.uk/car- ... T3026/1/38
Try ringing round your local parts suppliers, from memory, Parkers at Foundry square used to supply a lot of exhausts. 0116 242 8200
If you car has the original single piece exhaust it will need to be cut and have fittings added, or cut the flares off the new part and sleeve both sections.
If sleeving, it's best to weld the sleeve to one of the sections to make it a socket (downstream one works best as it captures the gas-flow), otherwise it will tend to sag at the joint.
A local welder, or exhaust centre should be able to weld on the correct joints for the new part to mate up to. It might even be worth approaching them for supply, but one would normally expect a mark up on price.