Sure looks like an Omaha Standard box. Same as on my 78 straight truck which has these rubber bezel's to hold clearance lamps. (pic below)

I found these which are not exact but might be close. Your hole is 3-9/16" or 3.5625" these are shown as 3.62" or just under 3-5/8" and might be able to work in your holes with a little help depending on the depth of the recess in the rubber mount for the  steel panel to fit into ?

Peterson & Grote are a couple popular names in lighting lens and fixtures.

https://www.easternmarine.com/truck-lite-3-flush-mount-grommet-10704

Also
https://www.ryderfleetproducts.com/truck-lite-10704/grommet-open-3-mount-for-2.5-lamp-p-u13-10704

Possible other sizes here:

http://www.truck-lite.com/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&urlLangId=-1&urlRequestType=Base&categoryId=13080&catalogId=10002

Please follow up if you find something that works as this would be helpful to others also looking for replacements.

(bezel.png)

bezel.png (53KB - 175 downloads)