It might be best to start with stock that comes from the U.S., unless you have already gone through the process of getting a permit (a “foreign phytosanitary certificate”) from U.S. customs to grow a tree from a seed/pit from another country, which it seems that you would likely need to do for this case. (For more information, please see:
https://www.cbp.gov/travel/clearing-cbp/bringing-agricultural-products-united-states
https://www.aphis.usda.gov/plant_health/permits/downloads/seedweb.pdf - this link talks about certain restrictions for Prunus, the genus that includes plums.)
In general, even though the species might be the same, seeds (or pits) from plants that have grown in one location may not adapt as well to another location, versus more native stock. Unless you are interested in plant breeding, then growing a plum tree from stock from a U.S. nursery might be more successful. Also, pits from fruit from a grocery store, for example, often come from varieties that are bred more for commercial concerns, such as shelf life and holding up during transportation, rather than traits popular for a backyard orchard, such as flavor. More varieties are available to home gardeners, too.
It might be best to start with stock that comes from the U.S., unless you have already gone through the process of getting a permit (a “foreign phytosanitary certificate”) from U.S. customs to grow a tree from a seed/pit from another country, which it seems that you would likely need to do for this case. (For more information, please see:
https://www.cbp.gov/travel/clearing-cbp/bringing-agricultural-products-united-states
https://www.aphis.usda.gov/plant_health/permits/downloads/seedweb.pdf - this link talks about certain restrictions for Prunus, the genus that includes plums.)
In general, even though the species might be the same, seeds (or pits) from plants that have grown in one location may not adapt as well to another location, versus more native stock. Unless you are interested in plant breeding, then growing a plum tree from stock from a U.S. nursery might be more successful. Also, pits from fruit from a grocery store, for example, often come from varieties that are bred more for commercial concerns, such as shelf life and holding up during transportation, rather than traits popular for a backyard orchard, such as flavor. More varieties are available to home gardeners, too.
Hope this helps!