I found them at the Specialty Tires web site. Through searching, it seems many vendors get their tires from this company which produces them. Link below to their site with various patterns and specs. The Industrial Deep Lug is under their Industrial Handling Equipment Tires section. They also have a range of military patterns used in the USA including the 7.5 x 10 Mule size.
http://www.stausaonline.com/
The specialty tire place only sells to dealers but they will answer tech questions and can also provide dealer company info for ordering. For me in Texas, the Wallace Wade Tire Company is closest even though I'll probably have them shipped to me. Still working out details but the wider cross section tire (7.5 x10 which is DF9C5) seems to be $135.87.