High Quality Sample Footage - Uncompressed

Hello,

I am working on a project to do some encoder quality benchmarking. To get the best results I'd like to start with the highest quality footage possible. Does anyone know where I can get uncompressed UHD (3840x2160) video? The uncompressed footage I can get is actually derived from some other compressed source such as ProRes, DNxHR, etc... For the most accurate test results, I'm thinking I'd like to avoid this.

Ideally this would be 10-bit and 4:2:2 color, Rec. 709 color space. They don't have to be long, perhaps a handful of 10 second clips would do the job.

I'm also considering using other footage, such as JPEG2000, Sony XAVC, or RED R3D as sources. These are more readily available. However, I'm uncertain if the compression in the source material will impact test results. Any input is welcome!

Thanks in advance!