Most tea kettles are right around 1.5 to 2 quarts in size. Finding much smaller (with a whistle) is nearly impossible, from what I've seen.
Le Creuset makes a 1.25 quart kettle. If you've electricity available, an electric kettle may be a reasonable option; they're not necessarily smaller physically speaking, but many will automatically shut off when the water reaches a boil, which does not take too long. A Sunbeam Hot Shot is another very convenient little electric water heater gizmo for a single cup; quick and easy and effective. If you're camping without hookups, these are of course less attractive.