(1) The quality of products sold in Taiwan is good.
(2) The quaility of the same kind of products sold in Japan is even better.
(a) The quality of such products sold in Japan is better than the same kind of them/those (sold) in Taiwan.
(b) The quality of products sold in Taiwan are good, but Japan's products are better.
Which of the above sentence is acceptable, (a) or (b)?
First of all, I don't think where one product is sold has anything to do with its quality. Its manufacturing would.
But strictly speaking of meaning, IMO (a) would make more sense, sinhce you are comparing the quality of the products sold in both countries; (b), due to its structure, suggests a difference in level: it is comparing the products sold in Taiwan with those manufactured in Japan (this last indicated by the possessive -'s used.
It could be that the regulations are stricter in one place so that manufacturers have to produce things to a higher standard to be allowed to sell in a particular market, but don't do it universally because it eats into profit margins.