Is There Any Numismatic Schools?

Sometimes Liberal Arts Colleges used to have programs that permit the student to design their own program for a degree with the approval of their advisers. That was how Donald Kagin and Jonathan Kern got their degrees (PhD and BA respectively) in Numismatics. They are the only two people I know of in the US with college degrees in Numismatics. There used to be a few universities in Europe that offered numismatic degrees but I don't know if any still do.

That's easy. Spend at least a decade working for a major dealer in positions of increasing responsibility, until they trust you to grade and make accurate offers to buy/sell raw coins whose value exceeds $10,000. In any category of US coinage. Or, establish and build your own company and grow it into that class of dealership. In essence, your best bet to become a professional grader is to become someone whose name is already known in numismatics first.

Or, move either to California of Florida, talk your way into a mailroom or administrative position, and spend the next decade-plus working your way up from the inside.