Some document retrieval services based in the D.C. area:
1. National Corporate Research (800-494-5225); goes to D.C.-area government agencies (including the SEC, PTO, National Archives), courts and libraries
2. Penco (800-690-7362 or 703-912-9080); specializes in retrieving legal and medical literature from D.C.-area libraries and government agencies (LOC, NTIS, PTO, etc.)
3. FSI (202-257-7722); courts and government agencies, also corporate records and UCCs
National Services that also work in the D.C. area include:
1. Thomson CourtExpress, formerly "FDR" and "West Document Retrieval" (800-874-4337); specializes in pick-ups from courts (including bankruptcy filings)
2. Business Law Research, formerly "GSI Document Retrieval" and "Westlaw Business" (800-669-1154), and ThomsonReuters Custom Research Services, formerly "Thomson Research Services" and "Disclosure" (800-638-8241); both specialize in retrieving materials from the Securities and Exchange Commission.
3. LexisNexis/WDS (800-728-5201); formerly the "Washington Document Service," but now headquartered in New York.
Library of Congress: See the "Document Delivery" section of the Library of Congress entry for companies that borrow books and get copies from the Library of Congress.
National Archives: The Archives posts a list of Independent Researchers Available for Hire arranged by subject specialty. National Corporate Research (800-494-5225) has been specifically recommended to me.