Most likely because you are choosing the chain stores full of idiots behind the parts counter. (i used to manage a advance auto). they can order it in, might not stock it but i know advance can order it. I just swapped a 6.9 in my gas 351 F350 crew cab long bed. I bought a coil of 3/8 and 5/16 to convert to low pressure fuel lines. Ordered from Carquest along with a filter head and filter with seperator drain to mount on the frame to do away with the known leaky stock unit.