Hi questionable_advice,
The latex itself is normally grown in plantations that are about 10 degrees north or south of the equator … mostly in SE Asia. You can see the top producers of raw rubber here and Sri Lanka also produces a lot of the natural rubber that is used in Dunlop latex cores that are seen in North America.
Most of the molded Dunlop cores are produced in the same countries and then shipped to North America. There are two factories in the US that produce continuous pour Dunlop latex in the US (Latexco and Mountaintop). Talalay is produced in the US by Latex International and in Holland by Radium who import the raw materials (either natural or synthetic latex).
All the Talalay (including 100% natural Talalay) would be from either Latex International or from Radium. There are about 5 or so main sources for most of the molded Dunlop cores you would see in North America along with the two manufacturers who produce continuous pour Dunlop (only one of which makes 100% natural Dunlop).
The brand name on a mattress means very little and a mattress is only as good as its construction and the materials inside it. There can be a significant difference in transparency between manufaturers and the quality of the materials that different manufacturers use inside their mattresses yes which is one of the reasons I suggest avoiding the major brands. In the case of latex … all latex is a good quality material but there can be a significant difference between different types and blends of latex both in terms of feel and performance and in terms of cost. There is more about the different types and blends of latex in this article and in post #6 here.
For the most part no except one of the latex manufacturers (Mountaintop foam) is owed by Tempursealy INC (the parent company of Tempurpedic and Sealy) and Pure Latex Bliss is owned by Latex International.
If the type and blend (natural rubber and synthetic rubber) of the latex is the same it will be relatively similar in terms of quality between manufacturers although they each have differences in how they compound and manufacture their latex (and the compounding formula they each use is proprietary and a closely guarded secret) so there will be some differences between them as well.
Phoenix