Most knives are not designed for throwing, and are not suitable for throwing, either. Their balance is wrong, their grip is wrong, and they are not designed to withstand the stresses of frequent impacts against the target, the ground, and other knives already in the target. But more importantly: they are designed for cutting, which is not a requirement for throwing knives, which only need a point.
To stress this: throwing knives should be blunt, except for the point. There is no need for a sharp edge, and it only leads to self-injury when handling, withdrawing from targets, or when throwing by the blade.
There are many, many throwing knives available from the Internet. We would recommend that you come along to SKATTA and trying throwing with our knives first, before buying your own. Our club knives are John Taylor throwers, designed by John Taylor of the main KATTA site in Pontefract, and manufactured in Sheffield. They are basic, cheap, and do the job really well, and make excellent starter knives.
For throwing, knives should be 12-18 inches in length. Knives smaller than this will rotate more rapidly, meaning that you will need far greater consistency in both judgement of distance and throwing technique in order to make them stick reliably. Twelve-inch knives tend to have a single rotation of about three metres, which also happens to be the competition distance for a single-spin throw.
Cold Steel do make a wide range of throwing knives, which are generally excellent (if expensive), aside from having ridiculously sharp edges. If purchasing Cold Steel knives, we would recommend taking a belt-grinder or similar device to the edge before use.