Originally Posted by
Jeff Wills
You bought handlebars which are the now-common "oversize" 31.8mm diameter at the clamp. What's in your bike now is the old-standard 26.0mm diameter.
My 1992 Trek 1420 (triple crank version of the 1400) came with 25.4 mm SR bars and stem so it's quite possible the OP's bars/stem are that size too. In any event, as you said, finding a quill stem for a 31.8 mm bar is not going to be easy.
One possibility is to get a threaded to threadless adapter ( like this:
Nashbar Stem Adaptor - Road Bike Stems ) and buy a threadless stem to match the bars.