When your customer wants specific textures and you can't find them. It's the most common problem in 3D design projects.
You can search for textures on the web and google images. But you need high-quality textures to get photorealistic 3D renders.
There is plenty of resource on the web but you need copy-right free textures. Because most of the creators sharing their works with license and most of them don't give permission for commercial works.
In the article, I will give you the names of the 3 best PBR texture resources.
Sharetextures.com is sharing their textures under CC0 Licenses.
They have 850+ free PBR Textures up to 4K resolution. Most of the textures are seamless and they are coming with diffuse, roughness, metallic, ao, displacement/height maps. You can find mostly architectural textures in their library.
CC0Textures.com great platform to get copy-right free textures. They have more than 1000 textures. Like number one, you can download these textures with PBR maps too.
Most know CC0 texture website :) They are only adding scanned-textures in their archive. Because of that Texturehaven only has 200 textures.
With these three resources, you don't need to worry about textures licenses anymore.