MUI X provides React components that extend MUI Core (or more specifically, Material UI). Some of the features are MIT licensed, and some are not. The version under the Pro plan can be purchased here.
⚠️ Please note: MUI X doesn't include any design assets. You can find design kits for Figma, Sketch and Adobe XD under the "Design" section.
Here are a couple of resources that you might be looking for: