Is it possible to find a webcam with large aperture? I'm looking for a Webcam with large aperture and shallow depth of field, similar to the F 1.8 Canon lenses, so far It has been really difficult since most of the specifications for any webcam are meant for home users.

I do video casting with green screen, and it does help tremendously having large aperture to diffuse the green screen (color evenness) and clarity at night with inexpensive lighting equipment. Also editing time is reduced considerably since I wouldn't have to re-sync audio and video or import files from the DSLR to my computer. 

Please give your thoughts.
Actually, your best bet is to use a PCIe or USB 3.0 HDMI input card, like a Blackmagic Intensity, which will take the clean HDMI output of many high quality cameras (e.g: a Nikon D600 or D800, a Canon C100 or C300, etc.) and make it available to other apps on your computer. This is what professional productions do for green screen work to ensure they're getting the full quality image out of the camera before it hits the camera's compression software.