I am a student studying AR with ARkit.
I want a variety of assets that can be used commercially. (there are limits to what I can do myself...)
Is there any place where I can get assets(like 3Dmodels, usdz file etc.) like Unity's asset store?
The resources on the Apple developer homepage are good but few, and don't know if they are commercially available.
For your first experiments with ARKit, Reality Composer might be a good start as it comes with a library of 3D models to load in your AR experience. Reality Composer is bundled with Xcode. For more content, I am sure there are resources out there in the web providing free models to download. Apple is also offering tools to convert models from other formats to USDZ. You can find them here: https://developer.apple.com/augmented-reality/tools/