Ben's Cycle in Milwaukee, WI sells the range of Nitto stems, which have a very wide range of sizes. Quality-wise, you can't get any better. (www.benscycle.net)

Weight-wise, these are not light, so your 280 g does not sound so bad. A Nitto Dynamic CrMo quill stem at Ben's is quoted as 294 grams, and a Nitto Pearl (top-grade cold-forged aluminum) is 325 grams. I don't believe vintage Cinelli stems were lighter. Modolo stems may have been lighter than these, but only incrementally so. There used to be Ti quill stems on the market and some welded ones made of sheet aluminum.

What is your old stem, and why does it need replacing? What size do you need?