Rear tyres are OT-66, good repros are made by
Marwan
As for the roll cage, they are very hard to find these days, and don't expect them to be cheap. You can pick up a runner Ultima for less than a new roll cage. NIP bumpers were available on ebay recently, priced at £18 each, and they sold out fast. For a roll cage expect to pay £50+ for a NIP one, £20-25 for a used one in good condition.