Does anyone know where I can obtain MS Visio templates (vsd files) with manufacturers products such as Xantrex, Outback, etc?

Unfortunately, there doesn't seem to be a database of these files anywhere.  You need to contact the manufactures directly.  There are DWG files available for manufacturer products which I think will be easier to get from the suppliers than Visio templates. Good luck with the search. If you do find a DB of the files, please let us know.