You may have to settle for whichever variety you can find raised from cuttings, at whatever size is offered. Or plant one of the wild Asian species raised from seed by a specialist grower like Colvos Creek nursery - when they have them - or grow your own.

Raising a cultivar from cuttings yourself might also be possible.

Since 'Shirotae' and 'Yoshino' are rather different, maybe you are not or need not be that particular about which kind you plant.