When people say you should learn standard English they just mean English that is grammatically correct. It's got nothing to do with being from the UK, the US, Canada, Australia or whatever other country you could think of that has English as the first language.
A teacher from any native speaking English country, and indeed some people with a high level in English from other countries should be able to teach you standard English. If you speak standard English EVERY native speaker will be able to understand you. There are some informal expressions that differ from country to country, but the standard form of the language is basically the same in each of these countries.
There isn't any such thing as a standard accent in English either. People use received pronunciation as an example of an accent that is easy to understand but there isn't a 'standard' English accent. When you speak English the important thing is to be clear, I wouldn't worry too much about imitating a certain accent.