Should I change my undergraduate thesis topic because of travel issues?
Some thoughts:


Can you collect oral histories without travelling to the US? For example, you can do interviews through Skype or work with a research assistant to collect some of the oral histories for you?
Why are you fixated on collecting oral histories? It seems to me that, in this case, the research question may be answered through some other means of data collection. For example, document analysis may be an alternative. 
It seems to me like your equating travel (or at least presence in a country) with the feasibility of your research question. I'm not sure that's appropriate. What would you do if you can't get to NZ, say because of visa or cost issues? Select a third country? What happens if you can't get into that country? Select a fourth?
Why are you intent on a bilingual thesis? There are a number of great South American wine manufacturers -- Chile, for example -- where you might apply the same basic research question.


Good luck!