i would recomend asimina triloba as coldhardy alternative to mango.
If you prefer seeds instead of a tree and since it is alreadylate in the season, there won't be time to coldy stratify the seeds. (they need 2-3 months + cold stratification) I would recomend a shortcut, i recomend placing lentil inn water for aday and giving that water to the pawpaw seeds. Combined with a warm cold place to sprout. The hormones out of the lentil will induce sprouting