These are Nitto Moustache bars, pretty close you what you want, but with a narrower straight section in the middle.



This is Nitto's North Road bar, more of a drop than the Moustaches, and the ends are angled outwards more, and straighter.



This is the Nitto Albatross, pretty much the same as the North Road, but with less drop I think.



Finally, there is this, which is either the Dove or the Chromo version of the Albatross (Rivendell use the same pic for both on their site).

I think these four are as close as you're gonna find off the hook, unless there are some wierd tandem or comfort bars that I haven't found. Obviously they're all designed to be used the other way round, and might need some trimming or even bending to get them spot-on, but it's either that or make your own.

Thanks to SJS Cycles, Harris Cyclery and Rivendell for the pics.