I'm having the same problem Andy.
Most of the bags that'll fit the lens plus camera are backpack in style, or alteast aren't quite ideal.
I was rather hoping I might be able to get a Billingham RocShoc bag...they did a couple for camera + 300mm f/2.8 and a larger version for camera + 400mm f/2.8.
I contacted Billingham, only to be told they don't make them anymore!
The tenba looked ok, but the wife (who's in the trade) has promised to make up a bag now that I have got together suitable materials and have a drawing and measurements of my ideal bag