Originally Posted by Iride01

If you are willing to spend the money, you can buy a new frame from most any bike manufacturer. Trek, Giant, Cannondale, Specialized and others all have a price posted for new and NOS stock they have in inventory. Some even tell you if one of their dealers (LBS's) have them in stock.

Definitely more trustworthy than any other used source. But I've bought from eBay, craigslists and others too. Just use a high amount of skepticism and satisfy those thoughts before opening your wallet.