They appear on eBay now and then, that is where I got mine. The listing was pointed out to me by a member here. And they appear in the parts section of this forum now and then.
If you
upgrade to the premium membership and support the forum, you can post want-to-buy ads. That is how I get the hard to find stuff in the easiest way possible. No guarantees but something to try.
I believe there are tons of these laying around in people's garages because the stock air cleaner, spacer, hose and flame arrester is one of the first things people rip off their new truck and replace with a chrome open air cleaner with chrome breather on the valve cover, baby chrome does get you home after all and the engine gets an extra 100 HP just for doing that! Not really, just kidding. But it does look so cool.