Buy them on ebay. They are extremely common and probably not worth faking I'd guess. Just look for a reputable seller based out of the east coast.
There are definitely replicas available that are labelled as such. I love how some of the genuine teeth are labelled "Brand New" and some "Pre-owned".
As others have said, ebay is great as there are a lot of good fossil dealers. I personally got mine at a flea market, and talked the seller down to $20 for something he probably just picked up off the ground.