There are usually a few people selling seeds and trees of Prunus Amreicana on eBay. It’s however considered to be invasive as it’s root suckers form a thicket. I planted two seedling Prunus Mexicana this year which is similar but does not sucker. For fruit quality you are better off with a Chickasaw plum if you don't mind the suckering. It will also form a thicket like Prunus Americana. All of the above are self fertile. I believe Beach plums are not self fertile.
I have two Gutherie Chickasaw plums which are grafted Chickasaw plums which do not form a thicket. They are in their second season and growing like crazy with lots of fruit set even in the desert.