Hi Willem,
Most likely, your are looking for a Moodle commercial partner. Go to http://moodle.com/partners/ and search for location "United States."
If others are curious about what "GSA schedule" means, answers are here. http://gsa.federalschedules.com/GSA-Schedule/GSA-Schedule-FAQ.aspx?gclid=COHXpoavgLACFUFo4AodYD_aGA