Volkswagen is considering selling CNG vehicles in the US. They already have the Touran minivan and Passat sedan available with the CNG option (the call it EcoFuel) in Europe. Hopefully they could make the transition to the US market without too much difficulty. 

http://www.ngvjournal.com/en/home/item/13361

VW's EcoFuel page (translated from German):http://bit.ly/19LPos6

Neat German video showing the Passat EcoFuel