First of all, you should know that when anyone is allowed to go backstage, the cast members warn you that it's a no-camera zone and no photographs are allowed. I know because I've been back there several times as part of Magic Music Days, performing in band. Second of all, you should know that it's not that picturesque anyway (that's the reason they don't want you to take pictures of it). I mean, granted, it's sorta cool to see shells of attraction vehicles, like bobsleds and logs and even tea cups, and occasionally an audio animatronic in some stage of being repaired in those huge warehouses, but that's about it.
If there is a site focused on this, I've never come across it, and it probably wouldn't be all that fascinating anyways.
I've done Magic Music Days, too. The backstage areas are fascinating if you're a Disneyland freak like me who doesn't mind seeing what makes things tick. But they would be totally uninteresting in any other context.
I'd love to be evacuated from a ride for once. It never seems to happen when I'm on the ride. For most people, that's the only way they'll ever get a backstage glimpse.
Backstage photos of Disneyland tend to mysteriously disappear from the Internet. It's kind of funny. I don't blame Disney for trying to keep those areas out of the public eye, but I still wish they didn't.
Most backstage footage and photography is terrible. Most of the people are either sneaking the shots when no CMs are looking, or they are CMs who see this stuff everyday and don't really care that much about the quality of the images.