Probably China

Look, there is no such thing as "polymerize" toner and thats it.
Just because it is CMYK powder, it's absolutely does not mean all toners are the same. The matter of fact furmulations can be different and unique not only from brand to brand, but between models as well. Magnetic properties and melting temp vary between toners for different brands/models.
Most of the canon printers use carrierless development process and toner just being applied on magnetic roller in developer unit. In Toshiba printers, as far as know, developer (iron powder) is being used that toner mixes in to and being carried to magnetic roller and released on to drum. The difference in properties of toner for both these techlogies are huge and if cross mixed toner will likely to just spill out all over the machine.
You have to buy make/model specific toner. With that being said, your question should be:
Where can I buy toner for
Canon such and such model
Toshiba such and such model
Now, keep in mind that usually, aftermarket toners are being developed for printers that use cartridges, i.e. cartridge that has developing unit and image unit built in.
If your canon/toshiba devices use toner cartridge that is just a tube/box with toner it is very very unlikely that anyone refills it but possible that you can buy those cartridges aftermarket if model is popular enough.