I stumbled across a Website that sells custom Roman standard poles and banners. You can give them your design, and they will make a nice one for you, or you can buy a common Roman one.
http://legvi.tripod.com/armamentarium/id251.html
(I have no association with the company but just found the Website.)
If anyone is interested in making banners for the Legion of the Binding Oath or the Legion of the Creeping Asp (Legio Anguis Reptatus), my primary PC has close relatives who have served as military tribunes in those legions (personal family backstory), and I’d be game to chip in to have banners made.
