You can split off a part of a forsythia or a lilac with a good sharp spade.  Both will generate suckers away from the main bush and those can be easily dug and transplanted.  It takes patience, as the new bushes may not bloom for a couple of years, especially the lilac.  Works well in the early spring or late fall, at least in Iowa.  Not sure if conditions may be different where you live.  When you transplant your cutting, make sure the new hole is 2ce as big as the chunk you're moving.  I try to use root stimulator (vitamin B12 solultion, available at about any garden dept.) in the 1st watering.  Mulch is a good idea around the new planting to hold moisture and keep weeds down.   When your lilac does begin to bloom, be gentle about cutting for bouquets the first few years......lilacs bloom on the old wood, so every bloom you cut will be one less for next year.  Good luck, and enjoy!!