You need to understand how powdercoat work. Powdercoat cannot do outside the workshop or in handy way. Like a spray paint or brush paint.

Powdercoat require high voltage charge unit, powder spray gun and oven.

So forget the powdercoat unless you takeout the whole grill and send to factory.

There is 2 way for you to get the same color (almost) from the shop.

Find a Dulux mix color shop. Show him the color code and ask them mix it for you.

or scrap a small portion of the paint out from the grill. show him the paint color and match the nearest wan out.

Mix paint shop have the color chart for you to match. Bring the color chart out to sunlight to match. Don't check under any light condition. It will give you wrong color match. (white balance influence the color K) 

To paint, scrap out the paint, sand out the rust. Paint a primer (antirust). Than finally your choice of color paint.

Fail to follow the proper way will repeat the rust again.