2002 CNG Van replacement parts

I have a 2002 Dodge Ram 2500 Van that runs exclusively on CNG. It's *not* a conversion ~ it was manufactured this way, in Canada I believe. Currently, the main control valve (I think this is the part) connecting to the gas tanks has sprung a leak & needs replaced. My mechanic tells me that the part alone will cost $600, and that they don't even make these anymore, so they'll have to modify a newer version of the valve to be functional on my van. My question is ~ are there resources out there for cheaper parts (I could've sworn I found one online for $420, but can't find the site now)? Is there any way to find the actual part itself instead of purchasing a new one that needs modified? How difficult is it to replace these things ~ my mechanic is unfamiliar with this type of fueling system, but willing to learn (and at this point, it's too late to have it towed anywhere else)? Are there repair manuals out there for my van? I've found them on gasoline-fueled models, but not on CNG vans. ANY suggestions or comments would be much appreciated. Thanks for reading!

try asking the dealer. if it was not a conversion and infact "factory" then the dealer should be able to get a part # on it and find it for you!