1968 Dodge Dart GT Convertible Latch Pin

Now that i think i have figured out what you are looking for...

Try McMaster Carr, Ace Hardware.

You might have to machine one yourself.

If (like me) you do not have a lathe, you could get some bar stock and chuck it into a drill and use a file to shape it. If you use staineless (not sure how it would cut with my method) you could polish it after so it looks a bit more chromed.

As for the knurling, you might have to come up with some other keeper setup. Maybe a set screw (use caution, cast potmetal is brittle)