Gas insert installation incomplete - need advice to finish it.

The firebox in our prefab fireplace sits about 5.5" above the hearth to allow space for the blower's intake vents. The direct vent insert we had installed (Jotul Katahdin) comes with only a 2" plinth, which is unsuitable to cover the vents. The custom black surround supplied by Jotul beautifully complement the fireplace on the right, left, and above. The rich black cast iron looks like it was there originally so the insert does not look like a retrofit EXCEPT for the exposed vents below. What we need is black metal about 5.5" wide, about 48" long and about 3" thick that will cover the vents and blend in with the Jotul surround. The installer has not been able to respond to this need. Any suggestions?

go to a sheet metal shop and get a piece of black metal. If yu need to match colors better get a can of matched paint from the dealer.

Thanks for the advice. I'll try that.