It might be worth investigating whether 2nd hand asymmetric kites from other classes might be approximately the right dimensions, e.g. Buzz, ISO, RS400, maybe even 29er. The seam lengths shouldn't really be that critical. One of the great things about the Cherub is that if your new kite has a slightly longer luff, you can just use a bit more pole length, or fit a longer bowsprit (for that generation of boat an old carbon 60 windsurfer mast used to do the trick). If the clew isn't in quite the right place, it's usually no big deal to shift the turning block on the deck.
