I asked around a little about a retro-fitting riving knife with mixed response....one older fellow, who's quite knowledgeable re woodworking, at my local HD said he thought Woodcraft or someone made a kit to retro-fit older table saws, but I checked with a local woodworking store he recommended and they said they hadn't heard of any...'yet', but he thought some companies might bring one out at some time.

Half of communication is listening. You can't listen with your mouth.