you should just be able to get the fitting itself. I heard that Scummit had them for $8, but its gonna cost another $8 in shipping. Your best bet would be A&E. I remembered just now when I was looking for the fitting, I went to Lee at United, he told me there wasn't an adapter and I had to drill out my fuel rail and tap it for a different thread

(this was 1996 or so)
You'd think Scummit and Jegs would have a "popup" for their ordering staff to sell the fitting when people order the gauge. I would have gladly bought one when I got my electric FP gauge, but forgot all about it (I need the same fitting so let us know what you find out)