Sorry, But I think that these bulbs are no longer available from anyone including Chrysler. I had a bulb (license) burn a few years ago on my Javelin and ran across the same problem. So what did I do??? I got a license plate bulb and lenses for a 68-71 Chevy Nova (I think). Not only did it go in without too many problems, but I managed to make it so if the bulb ever burns out, I can replace the bulb by itself. Granted it's not stock for AMC, you wouldn't notice it at a show or something like that. The only problem that I had while installing it was that I had to drill the bulb bracket at a different location.
So, if you don't want to go that route, keep an eye out for car swap meets, sometimes you can find that kind of stuff. At the AMC car show held in Kenosha, there was bunches of stuff, some good, some very bad. That reminds me, did you check to see if AMerican Performance or Kennedy AMerican had anything (just a thought)???