Not exactly sure what you mean, but I use a 14X23" griddle on my range that fits perfectly over 2 burners.
It is 100% nonstick after seasoning, will last 2 lifetimes and get better with age.

Its the Chef King griddle and on sale right now on Amazon for about the best price you will find most likely.

Here is a link that might be useful: Chef King Griddle on Amazon

If you want something aluminum and nonstickthis or this

If you want something uncoated, look for vintage on ebay or local thrift stores. Royal Industries makes one that is 15x23 but it is too big for what you want.

I used to have one something like this in cast iron.

Here is a link that might be useful: griddle 12x12

Thanks for the replies. Each of those looks like they would do the job. Just looking for something that will mate well with the Bluestar grates. Thanks for the suggestions.

Walmart sells Lodge seasoned cast iron griddles. Not sure if your Walmart has the really big ones. You can order direct from Lodge too. http://www.lodgemfg.com/seasoned-cast-iron/grill-pans-and-griddles.

I second the recommendation for the Chef King. I have the double burner model for by BS. I had the burners moved around so the two 23k burners are on the right side. This allows easier and more uniform heating of a griddle, which I use quite often.

The Chef King is heavy, but heats very evenly in my setup.