I just got off the phone with my friend who’s been repairing and commissioning forklift for a long time for a major shop and he said CNG forklifts are not a thing. Propane and electric are what is out there. Nobody knows everything but I believe he knows a lot about this. People confuse NG, LPG and LNG all the time but they are three different beasts. Maybe this is the case here?If UPS can find sources to fill the tanks for its forklifts all over the U.S you should be able to locate them too. Those outfits may not like your "looks iffy-to-them" tank. If you use the same tank as UPS does, they shouldn't have a reason not to fill it. There must be lots of CNG distributors who handle forklift tanks but who don't want to bother with "custom" boat-sized tanks. So it can be about the tank as well as the source. I've had propane dealers give me looks about our "mini" aluminum propane tank and have to be convinced too.