the only official reseller that i know of is http://www.applianceshop.eu/index.php/firewalls/opnsense.html others can sell it but can not charge you for the software. pre-configured anything are easier for anything as you have support from the person who sold it to you, they have to (US at least) provide some type of after sale support, not sure of the min duration though.
Are you the in house tech?
For support if you dont buy from them, theres the book and the forum and the main website for recommended min hardware as well as the official support from BSD Perimeter https://portal.pfsense.org/index.php/support-subscription, there is also support from other companies/individuals as well, so its up to you as to the route you choose to go.