Your Name and the 2 Gundam Thunderbolt movies have 4K BDs, but I don't know if they are upscaled or native 4K. There's also a Gundam F91 and Space Adventure Cob

Your Name and the 2 Gundam Thunderbolt movies have 4K BDs, but I don't know if they are upscaled or native 4K. There's also a Gundam F91 and Space Adventure Cobra movie 4K remaster, but those were animated with cells, so I don't know how useful those would be for testing an upscaler.