This is the trickiest part. Land owners can be asked, or suitable, quiet wild areas found. Wild Gardeners plant in any available green areas that they can reach, but it is much better to work with permission, if only because then the chance of the tree being allowed to grow to maturity are greater.
Churchyards, open areas in existing woods, persuade friends and friends of friends to accept trees on their land, your own garden.
This is an area of the website which will grow.