One of issues in North America with CNG conversions (like Diesel-CNG Dual Fuel Systems) is the lack of public refueling stations. Generally, public CNG stations run by natural gas utilities (NGUs) tend to have low priced fuel that follows the wholesale price of natural gas. Those run by Clean Energy Fuels tend to be relatively expensive because they appear to price their gas at a slight discount to the market price for gasoline. When there isn't a public station within a reasonable distance from your home base, you may want to consider putting in your own Vehicle Refuelling Appliance (VRA) or Natural Gas Compressor Package (NGCP).
Vehicle Refueling Appliances
Often, a VRA may be rented from a gas utility for a very reasonable cost. The advantage in doing this that the gas company is responsible for the maintenance on the VRA, which can be quite expensive. However, many NGUs do not have any NGV (Natural Gas for Vehicles) programs in place and, in these cases, you need to source your own VRA.
A popular natural gas powered car is the Honda Civic GX. It was originally marketed in conjunction with FuelMaker's Phill VRA, which was designed to refuel the Civic's CNG cylinder overnight. Honda very discretely bought FuelMaker Corporation and subsequently shut it down. Fuel System Solutions bought the assets of FuelMaker Corp. and appears to be trying to bring FuelMaker's products back on the market through BRC FuelMaker. FuelMaker VRAs (including Phill) are available through BRC FuelMaker's dealers. It is not clear how available are their VRAs because their web site states that: "BRC FuelMaker is committed to the continued production and support of the VRA and PHILL product lines. Both product lines will be back on the market in the near future."
Natural Gas Compressor Packages
For commercial fleets needing CNG, a low cost option would be to buy a used surplus public CNG compressor station but these stations often are shipped to other countries that actively promote natural gas as a vehicle fuel. New NGCPs may be purchased from North American companies such as: