go to subarupartsonline -- select the BRZ, then scroll down the list for the appropriate area; probably will say fender something. they are about 70 dollars each, total 140. pretty sure they come unpainted so you would need to go to a body shop for such; thats what I did for mine at least.
P.S.: i also think they come with the black plastic already on the pieces. don't be afraid to use force to pry them off. getting the 3mm residue off is a real bitch though. took me hours. goo gone helps
see
http://www.ft86club.com/forums/showthread.php?t=82037 for pics of how mine look on the car