I don't think it's possible to trade items between Wild World or City Folk anymore. I'm pretty sure the Wii and DS WiFi has been shut down. I'm not 100% positive, though.
But there is another way to get non-native fruit. Buy a lot of stationary and send each villager a one sentence letter with a piece of fruit. You will get either a shirt or a fruit. It takes some time, but eventually you will get all fruit. That's how I did it.