Ebay
You could check out the "For Sale by Owner" postings.
Local salvage yards, perhaps?
Make one yourself!?!?
I could be wrong, but I doubt you're going to find any new ones being made anywhere. SO, your best bet is looking around at the swap meets and online auctions and the like to find a used one. They used to be made, so they're out there. You'll just have to do a little sleuthing to find one....
... or is that what your were doing by posting here?