RE: .300 H&H Supplies?
As was mentioned if you have the brass and dies the rest is pretty easy to round up. Be sure to save every piece of brass you have for the H&H as it can be difficult if not impossible to find. It would not be easy to make from anything else either.
You have to decide what you plan to shoot with the rifle and then buy the bullets suited for that. If you father loads then he probably already knows that you need a loading manual, correct powder and primers