We had a foundary at DHs where they cast press tools. Whilst the metal used was not aluminium alloy, it wouldn't have been too difficult to melt a bit of scrap ally and pour it into a mold.
Sand molds are easy enough if your pattern-making is up to it, so the aeroplane could be an amateur job but I'm sure the stone part isn't. There's a lot of polishing required to get that finish on a sand casting of course.
I know a man who might know and have asked him . . .