US forest service goals is to protect land and forestry. Purchasing trees from this organization is not possible. There are other organizations that support purchasing trees for landscaping and sustainable communities. Most of these operate as non-profits and will include free trees with memberships.
USDA Forest Service and State Foresters
The USDA Forest Service manages forest issues in fire protection and fuels. They also research the impact of recreation on managed lands such as water sports, fishing, and hunting. Consult your local state forester to walk the land that you are considering landscaping or planting trees. Ask about invasive species and get referrals to local tree farms. Research the native species at the nearest university, or extension office to discern the type of trees which are already growing on the property in question.
Arbor Day Foundation
Trees provide clean air, shade and prevent soil erosion. The arbor day foundation supports planting trees on your property to assist with ecosystem balancing. Do not underestimate the value of trees that are dead on the property. Dead trees provide homes to insects, birds and small mammals.
Access to town or city utilities on the property requires you to be aware of things like gas lines and telephone poles when digging to plant a tree. You might need a permit in order to make extensive changes to the property. The local State Forester can best inform you of what is likely the greatest good for long term capital investment and stewardship.
Growing and Caring for Trees
Your state forester can tell you about how to prevent deer browse, or insect infestation of newly planted trees. They can also give you advice on the type of soil nutrients needed for certain trees to thrive and the synergy of diverse landscapes. While waiting for the trees to reach maturity, take note of water resources, light levels and any interesting habits of wildlife as years go by. Timber and logging may be a primary objective in planting trees, as wood products could be considered a renewable resource to replace fossil fuels with further research into cellular and genetic seedlings.