Mammoth Valley is a popular winter map, and a pretty high-quality one at that. I haven't tested it myself, though, so I'm not sure how up-to-date it is. Do be aware that it's more snow-centric than ice-centric.
There is a season pack that adds a spring, autumn and winter version to the east coast usa: https://www.beamng.com/resources/season-pack.7564/ And there is a polish map that has a winter version: https://www.beamng.com/resources/polish-roads-seasons-addon.15630/ However, you have to install the original map aswell: https://www.beamng.com/resources/polish-roads.5846/