We’ve discussed this color a few times on this forum. Here is one recent thread.
One modern color has stood out as a close match.
1996 Land Rover Richmond Green reference LRR635
I recently tried another source for the 1948-52 colors.
Select 1950 Jaguar and it brings up an old color chart for 1948-52.
I asked them how they would do Gunmetal.
They told me they had a formula for it, they would not just be matching this old chart.
I decided to take a chance and ordered a gallon of Gunmetal DBC-TCPD3106(K) lacquer, and it arrived about a week and a half later. Near as I can tell it is a good match to my original painted parts and what I had previously obtained from a local paint shop (who matched by eye).