Hi,
I'm not sure if you keep the Spanker in the UK, but I think it would be relatively easy to source a second hand alloy spar there, instead of trying to restore the oold wooden one.
You'd need a mast of app. 7meters, maybe from a discarded FD or Hornet or something similar. If it fits the mast gate in the deck, and your mainsail luff fits, you're fine.
I wouldn't exect you to appear at an official Spanker race, right
Gr, Arent
PS, If you are in Holland, try contacting the Spanker class association, they would know of any loose masts lying around in someones shed. You be amazed how many useful boat parts are gathering dust somewhere.....