If you need to source rudders fast the original rudders (the one without the T-foil, on the Stealth 'R') where stock 49ers rudders. I don't think the rudder cassette changed profile since then, just material (from aly to carbon).

Go visit your nearest 49er fleet and see if they have spares.

As for Dave's question about sailing without them keep in mind that Mark, reigning UK champion, uses rudders without foils on his Stealth...