Yes, I offer free choice Ranch Way horse minerals because they work with the local forage, not particularly happy that some are derived from petroleum products but it is hard to find supplements that are not
This farrier/nutritionist produces a good mineral supplement and I've seen many positive results with horses that are on it: http://www.californiatrace.com/

"It's really quite amazing what a horse will do for you, if he only understands what you want. 
And it it's also quite amazing what a horse will do to you if he doesn't." ~ Bill Dorrance