Apple in South Korea

You can google this: apple stores in south korea and you will find several.

We do not work for Apple, so we do not have information on Apple pricing. If you go in person and pay, the only tax will be the local tax.

Note: warranties for iPhones are limited to the country of purchase. If there is a problem, you may need to take it back to South Korea for service

I do not know. You will have to check with the government department that collects the tax (if there is a tax). I am in the US and do not work for Apple or the government so I am not familiar with foreign tax laws.