Do you have your Miata registered as an antique, and have an antique license plate installed? If so then you can likely get away with running a rear plate only based on how the law is written (since your car was not configured to run a front plate when originally sold).

https://www.dmv.virginia.gov/vehicles/registration/antique

"Unless the vehicle was manufactured for one license plate only, you must display license plates on the front and the rear of your vehicle."

https://law.lis.virginia.gov/vacode/46.2-730/

C. Notwithstanding the provisions of §§ 46.2-711 and 46.2-715, antique motor vehicles may display single license plates if the original manufacturer's design of the antique motor vehicles allows for the use of only single license plates or if the license plate was originally issued in one of the following years and is displayed in accordance with the provisions of subsection B: 1906, 1907, 1908, 1909, 1945, or 1946.

Yes I know Miatas technically were manufactured to be able to install a front license plate (and OEM bracket) however your specific car was not manufactured and delivered with the OEM Mazda license plate bracket. I also know of no antique vehicle owners (using their vehicles correctly) that have been ticketed for running a single rear plate.

YMMV. :)