Vendor for King Colorcore?

Try Piedmont Plastics in Richmond.
https://www.piedmontplastics.com/locations/richmond

 

Polymershapes sells King Colorcore HDPE.
They used to be called Sabic Polymershapes

 

I'm pretty sure you're just looking for standard engravers plastic signs. Rowmark, Gemini, Gravograph, IPI, and Southeast Plastic all mfg this type of product. Anyone that provides engraved signs should be able to help you with this type of project. You should be aware, the 1/8" material may be tricky to source. It's becoming less and less common due to cost. I often laminate two pieces of 1/16" together. It doesn't look spectacular after it's all done, but it's presentable and far more affordable. I do think taking the quantities into consideration, Gemini or Rowmark will take care of you but it may take a few weeks to get the material in.

One other thing, this material is surprisingly expensive to people in the sign industry. Per square foot, for 1/16" stuff, it's more than double the price of brushed silver ePanel ACM. 1/8" is more than 4x the cost per square foot.