When we first moved here I called some landscaping companies and asked to speak to a manager. They usually put me through to the owner as it is a rural area. I'd ask how they dispose of old landscaping materials like borders and if there was any way I could come relieve them of some of the materials. Nobody ever said no. I only called two and got what I needed for free, we just had to load it in the truck ourselves, and pick through it ourselves. I think in an urban area people may be concerned about a potential liability, someone falling or getting injured, but I guess it didn't occur to them or they didnt care.
We got some free landscape timbers, some edging material that we had to clean up and some red lava rock mulch that was scattered everywhere and we had to gather it, brush it clean etc.
If they had told me no I would have posted signs on the bulletin boards at the local grocery stores stating what I was looking for and would haul that off free for them if they were re-landscaping.
I have, many years ago, also talked to people at nurseries to find out what they do with plants they feel are past their prime, no longer saleable, and got some crepe myrtles for free that came "back to life" with some miracle gro.