It's probably worth getting a left and right side just in case. Or, you could try this place, they might have one used:

http://www.expolineauto.com/

Current Car: 2005 Lava Orange Mazdaspeed Miata 2004 Graphite Dodge Stratus Old cars: 2003 Garnet Mica Miata/1998 T-Red SVT Contour