Flying Objects do a triple without wheels and a single + sails with wheels. Weight of each is about 5.8.
I looked at those to replace the double NP I got but figured the savings in weight wasn't worth replacing it. My NP double weights 6.9kg.
The RRP for the triple cover is $325 from memory. You can email them at
[email protected] and they can let you know who has stock.
Or just ditch the bag. When I recently flew from Perth to Singapore someone checked in a surf board without cover. He had duck taped two thin strips of cardboard to the rails. The checkin chick at the counter just said: "You must be an optimist."