Most of the time, I try to buy my fresh produce locally, mainly from my weekly shop at the markets, because it is almost always fresher and of course, definitely a more sustainable way of eating. But sometimes, just sometimes, there are things which cannot be sourced locally.
Often found at asian supermarkets, but you have to hunt for them...and don't buy the dodgy ones. There are a LOT of dodgy ones...just use common sense, if it looks fresh, feels firmish and isn't infested with insects it may be ok. No gurantees though - it can be like an avocado. You know, it looks ok, feels ok but when you cut it open it's totally shit. But don't let that stop you from trying some star apple next time you see them.