Actually they do, in 1.74 index. Thats the highest index lens you can easily find, not just in photochromic but in clear as well. Tokai make a 1.76 but they aren't as widely available and I don't think it's easily available in a photochromic version.
Lenses of an index higher than that are only available in glass but not many people will pay for or want to wear those because of weight issues.
Please keep in mind though that a higher index lens doesn't mean it's a better lens even though they're more expensive. As a general rule the higher the index the worse the optical properties. The only thing higher index lenses are good for is that they can be made thinner due to the way a higher refractive index material bends light.
Anyway to answer your question I'm not aware of any great site for optical news. It'd be nice if someone made one. I sometimes have a look at the following sites.
http://www.optmagazine.com //this one is a bit sarcastic
https://www.opticianonline.net
http://www.optiboard.com/forums/
