how to get good at accent impersonations

Hi! That would be you and me both. What I mean is that Im looking for a way to at least approximate an American, British, or Australian accent myself. I am not a counselor in a camp but I really need it for my English class. We are required to lose out native English accent and try to speak English more like an American, British, or Australian. I have been trying to mimic dialogues on English movies but I think that wouldnt be enough. I dont know any American, British or Australian to converse with so I can practice my accent and I think the term would be pretty much over if I do a hasty migration.LOL We need it to get good grades in that English class and the first exam would be in July so Im crunching up on time actually. Well, at least your doing it for fun and so maybe you can accomplish that when you want. I hope you acquire those accents and have fun with the camp.^_^