The following archives holding Me 163 material have been identified:
Dasa, a.k.a. DaimlerChrysler Aerospace, formerly Daimler-Benz Aerospace. Dasa has an archives section at its main offices at Ottobrun, holding Messerschmitt, Bölkow and Blohm documents
Bundesarchiv - Abteiling Militärarchiv in Freiburg holds many military documents that must include Komet material. I've read that searching this archive is not easy however.
Imperial War Museum. A first inspection of the Duxford library turned up some Komet material. The MINTEC microfilm archive (a partial copy of the NASM archives) included some some structural dimension data. Another document found here was 'CIOS XXXII - 37: Messerschmitt Aircraft Design'. The 5,000,000 photograph collection is also likely to contain some Komet material.
The National Archives (formerly Public Records Office), London. Since late 1999, the PRO has an online search engine, which makes researching a lot easier. They hold at least some interesting documents on the Messerschmitt 163 and the Walter rocket engine.
Keele University has all existing RAF aerial reconnaissance photos from WW2 in its 'Air Photo Archive'. This collection should include Komet bases like Peenemunde, Bad Zwischenahn, Venlo, Brandis and Jesau.
National Air and Space Museum, Washington DC. There are a total of 457 Me 163 documents on microfilm reels, of which 34 are manuals. Also listed are a general parts list, consisting of 54 pages of tables (reel 2832, frame 1204) and a short Ersatzteil-Liste (replacement parts) consisting of 53 pages of tables and diagrams or drawings (reel 2499, frame 464). The collection is slowly digitized, and Bernard Biales found the following Komet-related online documents so far:
Captured German Aeronautical Documents (CGD) Microfilm - CGD-28: Me 163B Airplane Manual, Part 6 - Power Plant - Description, Part 7 - Power Plant Control and Maintenance, English translation, 27 pages
Captured German Aeronautical Documents (CGD) Microfilm - CGD-234: Theories About Tailless Airplanes, English translation of 'Theorien am schwanzlosen Flugzeug', 10 pages
Captured German Aeronautical Documents (CGD) Microfilm - CGD-245: Description of the Me 163B-0 Construction, English translation, 48 pages. Includes some performance figures.
Captured German Aeronautical Documents (CGD) Microfilm - CGD-256: Me 163, Volume II - Me 163B Airplane Manual, English translation, 297 pages
Iowa State University, Ames, Iowa. The ISU Library Special Collections Department holds the 'Alexander M. Lippisch Papers' that includes a lot of material that Dr. Alexander Lippisch took with him to the USA. The compiled a 113 pages listing, that mentions 100 boxes, 9 tubes, 6 mapcase drawers, 7 lantern slide boxes and 12 boxes of film. This most likely covers all of Lippisch' work, so only a part covers the Me 163. Identified were quite a few files on the Me 163 and its variants and testing.
Planes of Fame museum is said to have been given a complete set of Komet drawings by the NASM. The story goes it was one of two sets found on the German submarine on its way to Japan. The museum curator however cannot locate the set.
The Canada Aviation Museum has an on-line digital archive, that includes a fair number of Komet photos, mostly made during the restoration of the museum's Komets