I think the 25.4mm in the Nitto Technomic spec is the diameter of the handlebar clamp, not the diameter of the stem. I just measured my Technomic stem and the diameter (OD) is 22.2mm.

The part number for the stem for your Sports Tourer is Schwinn p/n 55 616, which has a 21mm OD (the old 13/16" standard), so if the ID of the steerer tube is larger than 22.2mm, the Technomic stem should fit. If you have to use a stem with a 13/16" OD, Harris has some, but they're not Nitto Technomic; Harris' part number is SM242 and they're only available with an 80mm extension.

EDIT - Well, the fork for your Sports Tourer (2097-C) is "For handlebar stems with 13/16" (21mm) O.D.", so I don't think the 22.2mm Technomic stems will fit.

According to the Sheldon Brown/Harris Cyclery website, "American-style bikes have thicker steerer tubes than Euro bikes, so they take thinner stems. The usual diameter is 21.15 mm vs the British 22.2 mm size. The stems listed below are this size. Sorry we don't have more to choose from, but these are getting scarce (these are the SM242 stems I mentioned above)."

I just checked the QBP catalog, and all of the 1" quill stems are 22.2mm, so I'm not sure what to tell you except maybe browse the web for vintage bike parts vendors looking for 21mm quill stems.