Yeah, I think you are right. Dunlop might be better for some, still they make less and less. Talalay is the new king.... It is probably marketing driven, just like the push to go "100% natural", albeit blended is a more supportive, longer lasting version. But "natural" is actually easier and cheaper to produce, and people can be easily talked into "going green"...
But I think I can help. You actually seem to have have two choices from the place what I've found.
1.
Twin XL 6" 100% Natural Dunlop Latex 7 Zone Core x 2 equals Standard King TwinXL-Natural-Latex-7-Zoned-Core
Regular price: $595.00
Sale price: $495.00
Made by LatexCo in Belgium
2.
Twin XL 6" 100% Natural Dunlop Latex Solid Core x 2 equals Standard King size TwinXL-Natural-Dunlop-Solid-Core
Regular price: $575.00
Sale price: $475.00
Made by Latex Green in Sri Lanka
Link to both:
http://store.mattresses.net/mefoov.html
They are in Arizona; shipping is not free, but still reasonable. No tax outside of AZ. When I called them they said that they have a promo going on, these cores are 5% cheaper right now.
I hope you'll find what you are looking for!