Some of the Greddy BOV's have odd sizes, just measure the diameter you need at both ends and order a silcone hose in a shape to suit your placement mate.
There's plenty of chinese pipes on ebay, quite a few suppliers to choose from online too so shop around.
Skiny and I have a local hydraulic hose shop that caters to the same stuff too which is handy. They supplied a hose for the last Greddy BOV I fitted, came from some sort of tractor and they had it on the shelf. Just needed a trim!