To bring this thread to a close, a quick update,
After having no response from Fox despite a couple of emails & the second hand one on ebay selling for £98 + £5 postage!
I researched similar sizes bivvies that i could find an alternative wrap from & took a gamble on the Fox EOS one man overwrap & pleased to report that it just fits my Royale Classic Bivvy.
Thought others might find this helpful as the Royale overwraps seem to have been discontinued.