You either have to be patient, until a new copy pops up on Ebay or another market, or put up crazy offers here in the hope that one of the current owners sells. There's no harm in making it known here that you are after a copy. IF one of the existing owners is contemplating selling, your offer may just be the thing that convinces them to sell
The secret to Atari collecting is patience You may have to wait 10 years to get one, but it will be worth it in the end!
Thanks for the advice. I'm definitely looking if any of you existing owners are contemplating selling. In the meantime, I guess I'll watch the auction sites and keep my fingers crossed.