I spent a few weeks asking around and searching for the same thing but ended up getting a mate in NZ to send a full Evo LHS shaft and three RVR 4G63T LHS passenger hanger mounts over.
With the RVR hanger mount, you simply remove the hanger from your existing GSR shaft, and then put the RVR hanger in its place -walah! fits the 4G63T block. You will also need a new bearing to go on the RVR hanger bracket when you do this but it costs under $10 from memory. Will see if I can dig up a bearing part number for you, but it opens your eyes to another alternative.