You can't buy regular clothes to fit this size doll. I have preemie baby clothes, and they are too big on our cabbage patch dolls...and I believe the doll you are speaking about it around that size.
I will say that Wal-Mart has a soft body/soft plastic limb baby doll (think, traditional style) that is HUGE. Literally, the size of a 12 month old child. We LOVE to dress this doll up, because baby clothes DO fit it...some 0-3 months, and some 6-9 month clothes fit it. It also fits into a size 3 baby shoe, which is adorable. This is probably my toddler's favorite doll, because it's so big and lifelike and wears real clothes and shoes. :) The doll cost about $13.