1992 Ford Ranger extended CAB smog issues

I bought from an elderly couple who took great care and I have owned for 5 years. No problems with smog until now. It will pass engine not gas. Apparantly I have the engien or fuel system that was only built for 6 months or so because of problems. The reason it wont pass is due to a plastic venting piece from gas tank, that is a dual not a single. Cant find part number and Ford dealer thinks i'm nuts. I have had my mechanic for ovr 15 years and trust him or he could have charged me for diagnositic and a whole bunch of money. Need help with part number and if even available has the state of California says I must fix
Thank you