Where I live, in the higher elevation, we can find thimble berries in the forrested areas. Kinda like raspberries, but much sweeter. We can also get cherry guavas and lilikoi (passion fruit), but I doubt they'd be good in this recipe. Poha is seldom found growing wild, these days. Whatcha find is usually farm grown and harvested. Once in a great while, a bird will "drop" some seeds from a "backyard weed" that produces a small, dark purple berry. Never bigger than 1/4" in diameter and heck if I know what they're really called. Locally, we call them popolo berry. Sweet as all git out and my daughter will eat the bush bare before they're all ripe.
Thanks for the description of that gooseberry. For some reason, I had the notion that it was akin to our poha. I read it on one of the forums, so I know the same or very similar berry grows on the mainland.