I've made some for an Esci 1/9 scale Harley WLA........
I sanded a domed profile on the end of a small-ish wooden dowel, then coated the sanded end with superglue - then sanded and polished that, to get a smooth, hard surface - I didn't want end grain marks in the plastic I was about to mold.
Then I heated styrene sheet over a stove element and stretch formed the plastic over the dowel (which I had attached to the benchtop with a small vice).
All that was left was to cut down the dome to the correct size. I drilled a small hole in the apex of the dome and glued a small, polished piece of clear styrene rod in the hole to replicate the glass bulb.
I used Model Master buffing aluminium for the reflector lens surface - it probably isn't as "bright chrome-like" as I'd like, but it's better than what was provided in the kit.