Straight To The Source

Here are some links to check out:

Agency-Specific Resources

Department of Agriculture 
usda.gov/da/

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Department of Commerce 
osec.doc.gov/osdbu/selling_to_doc.htm

Department of Defense
defenselink.mil/other_info/business.html

Department of Education
ed.gov/fund/contract/about/booklet1.html

Department Of Energy
smallbusiness.doe.gov

Department of Health and Human Services
dhhs.gov/osdbu/publications

Department Of Homeland Security
dhs.gov/xopnbiz

Department of Housing and Urban Development
hud.gov/offices/cpo

Department Of The Interior
doi.gov/osdbu/dbwdoi.html

Department Of Justice
usdoj.gov/07business

Department Of Labor
dol.gov

Department Of State
state.gov/m/a/sdbu/pubs/c13313.htm

Department Of Transportation
dot.gov/business.html

Department Of The Treasury
treas.gov/offices/management/dcfo/osdbu

General Resources

General Services Administration
gsa.gov

North American Industry Classification System
census.gov/epcd/www/naics.html