Everything was answered concisely in the first thread on this subject. You need to find a monument company that will mentor you through the process and help you find a supplier for materials. Expect a good bit of animosity when asking, because that seems to be the general sentiment when trying to break into any skilled trade.
Perhaps the best route is to find some who has retired from stone engraving. They would be more willing to answer your questions and help you get started.
If this will be your full time job, consider formal training. There are a couple of training centers here in the states that can help you.
JB