Where can I buy a concrete gate post in the style of this 1930’s gate post?
I don't know where you would buy it but it would be really easy to pour it.  Just build a box the size you want the post to be.  You could put any kind of medallion or symbol at the top of it.  Pour the appropriate amount of concrete in (probably 2 bags?) Then run a vibrating sander over the outside of the form or box in order to get any air bubbles out.  Let it dry and pull the form off.