Ask anybody you know if they have any in a spare bits box, Each new raider kit comes with 2 sets of sails and ravagers come with 3, there has to be someone at a local shop or something that would be willing to help you out! If not, well I can imagine them being a pain to scratch build. What might look cool would be to use acetate for the sails with some kind of pattern on them, semi-transparent with hexagons for example. But how to make the fins? That is tough. I would suggest creating a wire skeleton, attaching the acetate sails (or what ever else you want to use) to the wire with maybe ?superglue? then use greenstuff to bulk out the Wire and firmly hold the sails in place. I guess then either stick it on the boom with superglue or if your neat with greenstuff find a way to bond them together?
Its a lot of effort and personally I would just try to find repacements but if I couldn't, that would be how I would repair them!
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A very slow, 30K Salamander Distraction Log: VULKAN LIVES