When I had purchased my series 5 tail lights, (didn't read the description very well, ended up being convertible ones) they never came with the license plate lamps, when i search, they come up as miata/rx7 license plate lamps. Here's an example;

rx7 license plate lights | eBay

What I don't know is if the coupe lights will fit the convertible bracket, if the series 4 ones will fit the series 5 bracket, if they're all the same, regardless series 4 or 5. I need to get a set before I get pulled over

 

IDK but those Vert lights look good on the S4.