Thermoquad inlet fitting

Im having a horrible time finding the right fitting for the intet for my fuel line. From what I've read it's a 5/8x20 thread i need a flare nut for a 5/16 hard-line. Everything iv found is either for a 3/8 line, a 5/8×18 thread or for a rubber line. Does anyone know a good source for them?

I think the 5/8x20 is incorrect. All of them I know I believe have been 5/8x18, just like a Holley, Carter AFB or Edelbrock. I have several TQs if you would like a fitting.