100mm was the Campagnolo standard (including track) for front hubs. It was subsequently adopted as the ISO standard. Depending on the age, level and nationality of the hubs, things can vary a bit. For instance, most of the QR/hollow axle, French hubs from the 1970s boom are 96mm. And many of the inexpensive, steel, solid axle, Japanese hubs from the same era are 93mm. You may find even narrower examples, if the hubs are very old or a proprietary design. Of course, the fork blades can always be cold set to the required width.