The new aerials I've had from him did come with their posts, yes, but if for any reason these posts aren't exactly the same, he does a big selection of used boombox parts and would probably have something more model-specific.
He's a helpful sort of fella so it's always worth asking him what he can do for you.
I've attached a photo of one of the new aerials I've bought recently. As you'll see, this came with a post attached but it's the type that has a hole for a screw inside the box and what was needed for this job was the type of post that's held in by a circlip in a groove.
I sent him a message to ask whether he had any posts of that other type, explaining why I wanted these and he's sending a couple out for the cost of postage only.