Mine looks like anodized aluminum to me, maybe with a light sandblasting before anodizing for the matte finish. Maybe yours is painted? Anodize doesn't really chip off, it's actually the aluminum surface turned to clear aluminum oxide (rust) with black tint added. Aluminum oxide = sapphire, pretty hard stuff.
I send a lot of aluminum out to anodizing at the shop, it takes about three days. If it's anodized it'll need to be acid etched to remove the old anodize, then anodized. That's pretty standard stuff for anodizers, a lot of our aluminum extrusions come clear anodized and need to be black anodized for the optical test equipment we build. If it's painted you'll want to remove the paint, sandblast makes an even, flat finish. It's pretty expensive to send one piece, our anodizer charges a flat fee plus per-pound rate. I expect many machine builders and machine shops have anodizing done regularly, they'd send your spoiler with their stuff for a reasonable fee. Ask around. Or you could always have it painted, mine's black, pretty easy to match that.