People are shedding cells with DNA all the time, so it should be simple, in principle, to get a sample of anyone. If you have the right technology, this really can become simple. Find a hair, vacuum up some invisible skin flakes from someone's office, and there go, the raw material for a clone.

If you don't want it to be this easy (although one has to wonder why?), just make the sampling and extraction technology less reliable. Yes, you can get a DNA sample usable for cloning, but it will take a lot more work, tailing your subject for weeks at a time until the right opportunity arises, when you can engineer for them to "accidentally" prick themselves on something sharp and leave a drop of blood that you can get to within a few minutes.

There are adventure ideas in both scenarios.

Transcript

Luke: So Yoda, you're the only true clone?
Mark: {appearing} Not quite...
Mark: I'm your clone!
Luke: Whaaa? But... how??
Mark: Uncle Owen and Aunt Beru—
Luke: Oh, now it all makes horrible, horrible sense.
Mark: —wanted to keep you safe from any possible threat. The only way to be sure was to make backups.
Mark: The day they got you they sent a DNA sample to Kamino to have clone copies grown, ready to take over if required.
Mark: I've been studying your life. I know everything you know.
Luke: Everything?
Mark: {disgusted} How could you kiss our sister??