By now, there cannot be a woodworker, amateur or pro, who is not aware of what a riving knife is. And everyone is familiar with the long-standing tug of war between safety advocates who have wanted riving knives mandated and "the industry," which has resisted such interference. And most are aware that as of this year, all new saws sold in the U.S. must be so equipped.
What's "funny" (that is, strange, odd, etc.) is that U.S. made (or should I say "branded") saws sold in Europe have been required to have riving knives. But those same saws sold in the U.S. have not. Another "funny" thing is how resistant manufacturers have been to incorporating riving knives, claiming that the cost of their saws would have to skyrocket.
But if you look at the Sears Web site (just for an example), they have their "new" 10" table saw with riving knife listed for $249 and the "previous model" 10" table saw (the pre-riving knife version) listed for $229 (discounted to $149 on "closeout"). That is a higher price but not enough to be significant, especially since the "new" saw also includes the "blade guard-mounted Laser Trac system" and the revolutionary "Quick-release base clamping system" (allows for quick separation of base for easy transportation) which must have added at least as much to the cost of the saw as the riving knife.
Of course, this new standard still leaves a lot of saws out there that are lacking this simple device. And, unfortunately, it is not so simple to "retrofit" these saws even though the device itself is quite simple. So it is very unlikely that we will see any aftermarket or third-party attachments that can be mounted on existing machines.