Try running some searches.

I'm not all seeing, nor am I all knowing, but I don't know of any new information on natural bevel setters since this thread was active.

But with more insight into honing than I had when this was active, I really think you should consider the motives and results. For bevel setting, you want to have very consistent results; if you cannot get a great bevel, you will never have a great shaving edge. Bevel setters are where you do the bulk of your work, and thus where you spend the bulk of your time. This means the stone should behave in a consistent manner over long periods of time (single honing sessions) and should hold up to repeated use (many honing sessions) or else be easily replaceable when worn. These are all areas in which synthetic stones excel. Bevel setters are also the least expensive in each line of hones (as far as I know).

So you should really consider what your motives are for wanting a natural bevel setter before you invest tons of time (and possibly money) into finding one, testing it, learning how to use it, and learning how to make it reliable.

Just my .02.