Since I dont kniw the details, and yes, tastes are subjective, people (not necessarily you) are too quick to get rid if trees based on taste of one fruit or fruit off very young tree (sometimes first crops). With that said, good luck with the Oro Negro...for me, it is less appealing than its oarent the Monroe (which is unallealing to me too). Again, tastes are subjective.
As to Sweet Tart, try contacting Alex (Squam) at Tropical Acres to see if he has or will have any fruit for sale.