Which is correct: a Taiwanese corporation or a Taiwan corporation?

I think it depends on the usage. In convesational english I would say "company A is a Taiwanese corporation," using "Taiwanese" as an adjective. In a simiar way you would talk about General Motors being "an American corporation." But in contracts you usually see it written with the country name as a noun, not an adjective, to specify precisely where the company is incorporated. Thus you would see "General Motors, a US corporation," or in your case "Company A, a Taiwan corporation."