Find a dairy that has Jersey cows. Ask if they have any cows retiring. Buy cow.
The cow may be five years old and their milk production is on the decline but they will still produce milk for another five or more years.
Now you will want to breed this cow AI and choose a heritage size sex selected for a female.
The resulting heifer will be smaller then her mother, (easy birth yay!) and by the time her mom is really slowing down the milk production she will be ready to go.
Possible problems, they are generally not trained to be hand milked and it can take a bit to teach them. You want to make sure you do not get a "cull cow" which is no longer a breeder.
YMMV
Good milk cow advice!