Interesting, i still would try a store who has been selling the line who has been in business for a while. Some of the old timers remember everything.
Just remember, you can not unuse old worn blue jeans. You are using/enjoying a mattress in its 9th year of service. Even if you found the original mattress in an old timers warehouse brand new, never used, it may not feel quite the same as this 9 year, well used version of the mattress.
If customer service cant help, ask to speak to a VP of sales or someone higher up the chain that has been there longer, or as I mentioned, an old time kingsdown dealer.
Good luck searching,
Norm