Does anybody manufacture extra-wide (3E/4E or EEE/EEEE ) wide road or mountain biking shoes?
Sidi make a wide fitting version of their shoes.

I have a pair of Sidi's and they have been the best fitting, most comfortable shoes I've ever found. From their website:


  Mega sizes are cut with more material throughout, and a larger-volume heelcup. Mega sizes roughly correspond to a EE/EEE width on the Brannock sizing scale. 


Possibly still not wide enough for your needs but they're worth checking out.