Whenever buildings are torn down or raw land is developed, plants get destroyed.
For 19 years, I've done demolition and salvage work and I've been involved in moving about 50 whole buildings. Most of these sites have contained plants that would have been run over without my intervention. I dug a few of these myself, but more often I have called various landscapers and demo customers to take what they will. Several landscapers maintain a patch of dirt at home where they temporarily hold plants until they are needed. They often go into the ground in pots, so that they can be easily taken up when needed.
Native plants that require no watering or other care are popular with more enlightened homeowners. Whenever wild sites are cleared for development, thousands of plants get trashed. Around here, Oregon grape, salal and camas are popular additions to easy care yards. Mosses and ferns can be peeled from the rocks and transplanted. Often smaller rocks with a resident plant community can be salvaged rock and all.
Pond builders like these.
You seldom have to pay for this stuff. Contact the owner or contractor, dress for the job and stay well clear of any work being done. You may have to show up before or after work crews. With wild sites, you might be able to get in weeks in advance. Developers like good publicity. If you can see that they get recognized for helping to save the plants, you'll probably never have to pay for any of it.
Garden clubs along with adds on line are the way to
sell your plants. Landscapers need them too.