I don't know where the OP is located but MazToy in addition to the ones mentioned above are good sources.Check with partsgroup, 2nd chance roadster, I sell Miata parts, Mazmart, Flyin' Miata, etc etc. Or try your local junkyard.
Are you looking for an NA, NB or NC bumper? check the for sale section for partouts.
DAMN! **** has gone up since I replaced mine, but that was some 5-6 years ago for an NA. I wanna say I paid somewhere in the $180-$200 range but I can't remember for sure. That was just for the front bumper skin, that is what you're asking about right?I just called Mazda. I'm not willing to spend 430 on a bumper -.-