What is your exact question? Your subject line is not related to your actual post.
The answer to the question in your subject line is simple: you can't. The reason is quite clear: a time zone does not have a specific country; many time zones are used in multiple countries. For instance, CET spans half of Europe.
About your second question: you say you have the offset, right? You can then create an instance of SimpleTimeZone using that offset.
No you can't. Two good examples: the United States and Russia both span multiple time zones. In the end, there is a many-to-many relation between countries and time zones: a time zone can span multiple countries, and a country can span multiple time zones. The only way to get the correct time zone is to know the exact location; that is, the longitude and latitude. Some time zones do not run in parallel with meridians, so only the longitude is not enough.