I did highway signs, stripes, and all else one summer…the signs we made were of a reflective green plastic laminate that was melted onto the metal. The letters and numbers in white were done the same.
The stripes are sprayed w/ either a latex or rubber based paint usually very fast drying and the beads are simply small clear “glass” beads that are sprayed on top of the paint.
When touching up a job I would often use a roller or hand sprayer and then throw beads on top by hand.
Try the yellowpages in your local area and call someone who does stripes, barricades, etc. “Safety-lights” is one name that comes to mind. They would have the materials you seek.
I worked at Sherwin-Williams in highschool and they used to sell a reflective paint, but that was then. They did have reflective spray paint at one time but…I don’t know anymore.