Apologies in advance but I did not know where else to put this.

Does anyone know of any repositories or sites which provide existing XML DTDs for download? Not necessarily related to Games

Someone asked if they could download a DTD for an existing file type that uses XML. They were not looking for any file type in particular, they are building an application that is essentially a Calendar and they wanted to know what existing XML based file types existed and if their DTD were downloadable. This original question is not relevant anymore what we now just want to know, as the title of the post says, is there an XML DTD repository or collection that anyone knows of?