Do you mean just the quick release skewer or the actual axle of the hub? Skewers are easy to replace, just find the right diameter and length (probably 9mm and 100mm for a standard QR front). You can get replacement axles for the higher end hubs but there are so many different models of lower end that chances of finding one are slim to none. And even if you find one, you need someone with the skills to swap and adjust the bearings. Overall probably cheaper to buy a new hub or even a cheap front wheel.