Option #1: Subdeacons can order a full set of deacon's vestments and request to have the cuffs omitted (deduct $75 for no cuffs). They then wear the sticharion with the orarion crossed in the subdiaconal fashion. Please see the Deacon's Vestments page for the various fabric options.
Option #2: Subdeacons can order an altar server's robe and a subdeacon's orarion (15 feet long by 4 inches wide). These vestments are for subdiaconal use only; they cannot be "converted" into deacon's vestments. Please see the Altar Servers Robe page for fabrics and colors available.