I made one for my XR (and now CRF) out of a spare piece of 1" webbing tie-down strap. Simply find a suitable length (I doubled it over for additional strength), then use a small soldering iron to melt a bolt hole through each end (double over the loose ends to avoid fraying). Keep this hole as close as possible to the size of the bolt thread. While the melted nylon is still hot and plyable around the new hole, press it flat with a hammer or similar to provide a solid mounting point. Use a large washer under the mounting bolt.
Bob's your uncle in about 10 minutes, and £20 more beer tokens in your pocket.
Thanks Big T. No spare webbing straps or similar in my garage, so ordered a Kreiga for £19 with free p&p, but thanks for the tip. Might well make one next time!