The Housing and Urban Development in their Grants Available page makes it clear that they do not provide grants to individuals -- hence no grants for a person to buy a home or land http://www.hud.gov/grants/index.cfm
"While HUD does not offer direct grants or loans to individuals, we do work through local governments and non-profit organizations to make financial assistance and counseling available."
You can go to the Catalog of Federal Domestic Assistance (CFDA) http://www.cfda.gov and Grants.gov http://www.grants.gov - these are two FREE sites created by the federal government to provide transparency and information on grants. Browse through the listings and see if you can find any grant that would support your purposes.
Go to CFDA http://www.cfda.gov --> Search for Assistance Programs (HTML) --> Browse The Catalog By Functional Area --> Click on HOUSING --> click on Land Acquisition and these are the available grants http://12.46.245.173/pls/portal30/CATALOG.FUNCTIONAL_PROGRAM_TXT_RPT.SHOW?p_arg_names=func_cat_cd&p_arg_values=MU :
10.405 USDA Farm Labor Housing Loans and Grants
10.410 USDA Very Low to Moderate Income Housing Loans
10.411 USDA Rural Housing Site Loans and Self_Help Housing Land Development Loans
10.415 USDA Rural Rental Housing Loans
14.127 HUD Mortgage Insurance_Manufactured Home Parks
14.130 HUD Mortgage Insurance_Purchase by Homeowners of Fee Simple Title From Lessors
14.168 HUD Land Sales_Certain Subdivided Land
14.218 HUD Community Development Block Grants/Entitlement Grants
14.219 HUD Community Development Block Grants/Small Cities Program
14.511 HUD Community Outreach Partnership Center Program
14.866 HUD Demolition and Revitalization of Severely Distressed Public Housing
15.124 DOI Indian Loans_Economic Development
I don't think there's anything for your purpose.
Grants have objectives, and the grant applications that best captures the grant's objectives are approved.
There is a stringent review process through a committee composed of federal employees and selected experts in the field. You will compete with other applicants for the grant money, and this grant review committee will evaluate the merits of each proposal. Only those that they feel exemplifies the objective of the grant will be approved.