My go-to approach is to start with sites that explicitly offer public domain or CC0 content, because I like the peace of mind that comes with a clear commercial-use label. Pixabay, Pexels, and Unsplash are great first stops — you can find high-res cherry blossom photos and some vector art that are free for commercial use. For true clipart vectors I often check Openclipart and PublicDomainVectors; those tend to be CC0 or public domain. Wikimedia Commons also has older illustrations in the public domain if you search carefully.
Always read the license on the specific file before using it commercially. Even sites that host free content sometimes allow uploads under different licenses, and some contributors require attribution. Look for SVGs or EPS files if you want scalable clipart; I usually open them in Inkscape or Illustrator and recolor or simplify line work. If a file says 'free for commercial use, no attribution required' (or CC0), I’ll feel comfortable dropping it into a product or print project.
One small habit that saves me headaches: I save a screenshot of the license page and the download page alongside the file, with the URL and date. That way I can prove I checked permissions later if needed. It’s a little extra work but worth it for peace of mind — I love seeing cherry blossom art come together in a project, and that small step keeps everything chill.