It's been talked about a little bit online before. The ones in the photos you see the guy basically surgically took apart several disposable diapers and pieced them together. He only does it for people he knows personally, so no commissions like you said.
There was a website in the US called fundiapers that did something similar but not as high quality, but they shut down. I've also seen a guy on tumblr whose name I can't remember right now who makes some custom diapers himself but again, he doesn't take commissions.
You could do this sort of thing yourself but it would take several diapers for each one and be crazy time intensive and probably require a painstaking attention to detail.
The reason no one does this for pay is because there's no way it'd be worth it for a disposable product. But someone who's wearing them just to model them online will get them for nice pictures.