So you need gaiters to fit over what are basically ski boots. Correct? And, no, most gaiters won't do that—they'll fit over regular mountain boots or leather boots, but ski boots are bulkier.
With that in mind, I think your best bet will be a pair of Outdoor Research Expedition Crocodiles ($84, www.orgear.com). These are like the popular "regular" Crocs—a Gore-Tex gaiter with a wide hook-and-loop closure along the front—sized for big boots and bulky clothing. In other words, they have a bigger girth than regular gaiters, so they'll fit over ski boots and your ski pants. I've worn Expedition Crocs over Scarpa Inverno boots with lots of extra clothing and had room to burn. Ski boots shouldn't be a problem.
You might also try Black Diamond's Termigaiter2 ($40, www.bdel.com), which is specifically designed to fit their ski mountaineering gear. The Durastretch nylon/Lycra fabric ensures a comfortable, light fit, while its simple hook-and-loop closure makes it compatible with a variety of boots.