I ordered the plug online but don't remember who from. I think I know where they are in my back garage and they are still in the bag they came from and there should be numbers on the bag. Gray is their natural color, close match. I will get back to you Mendel.
I found the place I ordered my center caps for my 2016 Prius wheels. I put a little dab of hot glue on them and tapped them in. 1EMR6 Knockout Plug, Hole D 2 In, PK 10 - Walmart.com