Unfortunately schemas for the various models (and their variations over firmware versions/time) have not been published, and I'm not otherwise aware of how to find them. They are defined internally by what amounts to a custom schema definition language, and the definition files are not accessible. About the only suggestion I'm aware of is to create one of each device type you need to support on a live UCM and retrieve the XML via AXL.
It might be possible to get a dump of these definition files for a given version...attached are the 'display instance' file for 7960 and one of the 'rules' files that define the validation rules for the fields. Let us know if this type of info would be helpful.