A thought for public gardens: offer a cutting tour. Charge a reasonable fee, tour the gardens giving the OK or not to take cuttings from certain plants, perhaps have baggies and snippers available. Oversee the snips to preserve the health of the plant. Use it as an educational tool.
On a similar note, what are thoughts about taking, or not, seedheads from the wild, parks, or private gardens?
I regularly poach seed and young seedlings growing in the ditches because I know the County will annually scrape the ditches clean, so I don't give that any particular thought. On my road, I've harvested digitalis seed, sword fern, salal, and snowberry (all destined for the backhoe).
I've often thought the Boy Scouts (or similar organization) could dig up and sell evergreens and shrubs that are growing too close to the road along the shoulder of our mountain passes. Good fundraiser for them, repurpose the plants, seems like a win-win.