A kosher esrog during sabbatical year

Which esrogim (citrons) is one allowed to use on Succoth on a sabbatical year?

Since an esrog is a fruit, it acquires the holiness of the sabbatical year; therefore, it’s forbidden to sell esrogim commercially. Thus, this year there are three options:

1. Buy an esrog through Otzar Beis Din (which charges only for maintenance/delivery of esrogim, but doesn’t sell the esrogim themselves).
2. You yourself can pluck an esrog in a field that was declared ownerless according to halacha.
3. You can buy an esrog that was grown outside Eretz Isroel.