http://www.matrox.com/graphics/en/gxm/products/dh2go/home.php
But they aren't cheap.
I've suggested the analog one because the digital output on a MacBook is limited to 1920x1200 - probably useless for yourself (assuming your screens are 1280x1024, your total resolution would be 2560x1024, quite a bit over the limit).
I'm sure that the analog goes high enough to support your screens... But don't quote me on it, just in case.
😛