I had a quick look, and it seems that XSDs are freely available for all UBL types (for UBL version 2.1 you can find them here: http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd). So the easiest way will be to import the required XSDs into an E2E model. Just make sure you import the UBL version expected/used by your Navision installation. I am not aware of any project in E2E that uses UBL right now.
Hope this helps,