The weather icons that are in the documentation/sample are primarily for reference purposes. I'm only aware of those PNG versions and haven't come across any SVG or larger scale versions. I don't recall any images being 1000x1000 and don't see any such images in the github repo of the sample site. Generally, companies prefer to use their own set of icons that are more in line with the style of their website.
The Weather services in Azure Maps are powered by AccuWeather, so you could also look at using their icons: https://developer.accuweather.com/weather-icons
For reference to others who see this thread, here are links to the docs/samples that use the reference icons: