I just posted a NIB one in the trading post section last week. It was listed on CL in Yakima, WA. I bet its still available.
The grates & griddles in the older gassers are the same parts that came in the set you're describing. Believe it or not, you already have the most elusive part, by far.
BTW, I have a nib one also, which is why I didn't jump on the Yakima one.