Well...
You can shim a headtube down from 1 1/8" to 1", then get a threaded fork and headset in that dimension.
Or you can keep your existing fork and headset. Use an 1 1/8" ID seatpost clamp to hold the headset preload. And the quill stem of your choice. 1" stems can be shimmed to fit 1 1/8" steerers.
You need to figure out a way to set the headset preload. I think Sheldon Brown has tried and writen about that too.