like the trees in Washington DC?

They are sterile. They don't produce seeds. If you live anywhere (except the
Southwest) in Zone 6 or warmer, just go to a nursery & ask for a 'Kwanzan'
cherry. However, that variety is not especially good for bonsai. If you want
something similar, get 'Hally Jolivette' or one of the species cherries.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"When you come to a fork in the road, take it." Yogi Berra