Mimosa or Silk tree (Albizia julibrissin) seeds are fairly easy to find and grow. Try the seed exchange forum here at GW or collect some of the abundant pods they drop or check online for a source.

Soak the seeds in warm water for 2 days or so. Some suggest scarification, but the soaking should be enough. plant in normal potting mix. be aware this tree is considered invasive by some.

When I lived in Phoenix I would just go to the park and pick some up of germination experiments. Gardenweb has a Gardening in Arizona where you might locate someone to do the same for you. My experience was that you get better results from fresh seed, late summer or fall, and you get better results scratching them with a nail file. But the seeds do germinate rather well when a year or more old and just soaked or planted.