You may be able to find the below books at a library near you by checking out worldcat.org. The second line tells me where to find the book in S.Cal. The asterisk (*) indicates the books I have reviewed.

*Adkins, Hal. Directory of Homebuilt Ultralight Aircraft. Haljan Publ. 1982.
    Cal State, Long Beach, +Link. Has pics plus specs.

*Aircraft Shopper's Guide. 2004. Cybair Ltd. P.O. Box 42, Richford, VT 05476.
    My Library

Baughn, Terry V and Johnson, David B. Structural Design Considerations for Ultralight Aircraft. SAE, 1986.
    Explains cable support vs. strut support when converting in ultralight aircraft.

*Beaujon, Herbert. General Design Requirements. Available from author.
    My Library

*Burger-Burr's Ultralight and Micro-light Aircraft of the World. Haynes and Co., Ltd. England, 1983 & 1986.
    My Library

*Campbell, Jim. Flyers Guide to Ultralights. Tab Books, Inc. 1985.
   Co. L.A. Public Library in Downey, Ca., San Jose Public - +Link. Gives pilot reports.

*Campbell, R.D. and Jones J. The Micro-light Flying Manual. Granada, 1982.
   Cal Poly, Pomona.-+Link.  Good sourcebook.

*Carpenter, Carol and Brian. A Professional Approach to Ultralights. Rainbow Aviation Services, Corning, Ca. 2003.
   L.A. Publ Lib.

*Chipman, Doug. Flying Ultralights: Instructional Briefings. Aviation Supplies & Academics, 1995.
   Berkeley Pub. Lib.

Collier, Larry. Building & flying the Mitchell Wing. Tab Books. 1982. p. 176. ISBN 0830623027.

Cook, David G. Ultralight - Design and Construction. Can't seem to track this down.

Cook, David G. Flying from my mind: Innovative and record-breaking micro-light and aircraft designs. Barnsley: Pen & Sword 2007.
    Palmdale City Lib., Library of Congress.

*Coombs, Charles Ira. Ultralights: The Flying Featherweights. NY: Morrow, 1984.

Cosgrove, Brian. Ultra Light Aircraft and the Air. Airlife. 1980. There is some confusion on the publication dates.

*Cosgrove, Brian. Micro-light Pilots Handbook. Crowood Press, Ltd. 2002. Great sourcebook.
   L.A. San Jose Publ. Lib.-+Link.

*Jane's All the Worlds Aircraft. (Especially 1976-1986 for classic ultralights)

Drisdale, Tommie and Hanes, Steven. The Ultralight Aviator's Handbook. Skyflight International, Inc. 1982.

Dwiggins, Don. 31 Practical Ultralight Aircraft You Can Build. TAB Books, Inc. 1980.
    Riv. Publ. Lib. Hemet Publ. lib.

Finigan, Chris. Micro-lighting: Affordable Aviation. Crowood Press, 2001.

Heintz, Chris. Flying in Your Own Wings: A Complete Guide to Understanding Light Plane Design.
    Wonderful articles by Mr. Heintz are located at http://www.zenithair.com/kit-data/ht.html.

*Hovey, R.W. Ultra-light Aircraft Design. 1976.

Hovey, R.W. Fun Flying. 1981.

*Kimberley, Gareth J. Fun Flying: A Total Guide to Ultralights. Tab Books. 1984.
   S.B. Publ Lib.

*Markowski, Michael A. Ultra Light Aircraft. the Basic Handbook of Ultralight Aviation. Ultralight Publs, Hummelstown, PA, 1983.
  Riv. Pub., UCR, Cal Poly, Pom.

*Markowski, Michael A. Encyclopedia of Homebuilt Aircraft. Tab Books. 1979.
   Cal Poly, Pom.

Markowski, Michael A. Ultralight Aircraft. Ultralight Pubs. 1982.
   Riv. Pub., UCR,

*Markowski, Michael A. Ultralight Flight: The Pilot's Handbook of Ultralight Knowledge. Ultralight Pubs. 1982.

Mattern, Joanne. Flying Ultralights. Roarke Pub., 2010.
   Hemet Pub. Lib.

*Millspaugh, Ben P. Ultralight Airman’s Manual. Tab Books. Blue Ridge Summit, PA, 1987.
   Riv. Publ., U of Redlands, Riv. Co. Lib.

*Mrazek, James E. (Jr. & Senior). Ultralights: A Complete Introduction to the Revolutionary New Way to Fly. St. Martins Pr.1983.
   Azusa City Lib., Crowell Pub Lib in San Marino, Ca. San Francisco Publ. Lib. - +Link.

*Pagen, Dennis. Powered Ultralight Aircraft. Black Mountain Books. 1980.
   My Library.

*Pagan, Dennis. Powered Ultralight Training Course. Pagan. 1981.

Raymer, Daniel P. Simplified Aircraft Design for Homebuilders. Design Dimension Press, 2003, 143 pages.
   S.F. Publ. Lib.

Riding, Richard T. Ultralights, the Early British Classics. P Stevens, 1987.
   San Fran. Airport Museum. Library of Congress. Airplanes built in Britain between the Wars when low-powered engines meant that most aircraft
        were  'Ultralights'.

Stow, Chris. The A-Z of Micro-lighting. Crowood Press. 2006.
    Idaho Falls Pub. Lib.

*Taylor, Michael J.H. Jane's Pocket Book of Home-Built Aircraft. Collier Books, 1977.
     No ultra-lights included.

*Thorne, David, Micro-light Flying Machines. Aero-Fun Publications. Salida, CA, 1981. One book has 75 designs and another 120 designs.
    Lib. of Congress and wouldn't send out on interlibrary loan. My Library.

*Welch, Ann Courtney Edmonds. The Complete Micro-light Guide. E.P. Publishing Ltd. 1983.
    Cal Poly, Pom.