Ive lost a couple over the years. As they're quite pricey to buy from Mazda, what I did was to cut a strip of the same size as a remaining cover, from an ice cream plastic carton lid, painted it with my touch up brush and stuck it in place with blue tack. You cant notice it unless you stand by the car and look directly at it. Ive never had one of these pinched!!
Much better than forking out pounds for a similar bit of plastic that will probably go missing in time anyway!!!