I was looking for a good source for 4" diamond wheels.
Try Diamond Pacific,800-253-2954. They make some of the best diamond
wheels in the business.
Another possible source is your local dispensing optometrist. Many
times shops that grind lenses for eye glasses have wheels get damaged
or contaminated by a large piece of grit. When this happens, they
can’t be used for grinding lenses, but are perfectly good for rocks.