Whatever happens, you purchased the home from the park owner and his ultimate responsibility of the condition of the home will always remain. Indeed, that he cannot obtain a Gold Shield Warranty on the property leaves him quite vulnerable in my view.
So far as a warranty per se is concerned, Gold Shield are not the only organisation who cover new park homes. Perhaps if the owner puts himself out a little he will establish others in the market who offer a similar if not altogether more comprehensive cover.
You were clearly misled when you purchased the property in believing there would be a Gold Shield cover on the home. Your owner is in breach of that element of the purchase contract.