The newer, more trade-oriented, publications are likely available through a local bookstore on special order or from your favorite on-line bookseller (i.e. Amazon, Barnes & Noble, etc).
For used and out of print books, searchable databases of titles on offer from thousands of antiquarian booksellers may lead you quickly to the book you are seeking, sometimes with a surprising spread in prices; I have had good experience with the Advanced Book Exchange and Bibliofind (which is now part of Amazon). One word of caution about these databases: some dealers are slow to negligent in removing what they have otherwise sold from the listings, so don't assume you have really found it until it is confirmed, but most dealers are diligent.
A specialized book dealer, particularly in the relevant geographic area, is likely to be of assistance in acquiring out of print works and academic publications. Specialized dealers whom I have used include:
Boekhandel De Verre Volken within the National Museum of Ethnology at Leiden in the Netherlands carries a large stock of new and out of print books on the material culture of non-Western civilizations, including many arms and armour titles. They ship world-wide.
David Brown Book Company (in the United States, Oxbow Books in Great Britain) carries a large stock of more recent academic publications on archaeology from prehistoric through to the Middle Ages.
John C. Denner Co. of Box 122 - RR 1; North Lancaster, Ontario; Canada K0C 1Z0 (Phone: (613) 525-3840 and Fax: (613)525-1865) carries an extensive selection of new and used books as well as a wide range of antique arms and armour.
Ken Trotman, Ltd. of P.O.Box 505; Huntingdon PE29 2XW; England, telephone 01480 454292; telefax: 01480 384651 (from the US, dial 011 44 and omit the preceeding 0 from the British expression of the number) specializes in both new and rare out of print books on weaponry and military history. Alternating catalogs of "new and forthcoming" and "fine and rare" books are issued three times yearly. I'd recommend submitting a want list for rare or out of print titles as I have found that they are frequently sold by the time the catalog is received (in America). E-mail to email@example.com. An obvious first call for British material.
Very little appears to be published about medieval swords in the English language collector oriented publications with which I am familiar; most of the sparse opportunities which do arise are in scholarly publications usually in languages other than English (I suspect those fluent in German would find many opportunities).
The Catalogue of the Park Lane Arms Fair is published annually as the program for this single day event. Back issues of most are available from the show's organizer.
The Gun Report, P.O. Box 38, Aledo, IL 61231-0038 USA, telephone (309) 582-5312, is more fully oriented to the typical American collector's focus on firearms. From 1985 to 1988 they did publish a series of articles on swords from prehistory until the close of the medieval period by Ewart Oakeshott, but sword oriented works have been rare since.
The Journal of the Arms and Armour Society, (£15 yearly - two issues as a benefit of corresponding membership in the Arms and Armour Society of Great Britain) is stongest in scholarly articles about 18th & 19th Century gun makers and has contained surprisingly little on the subject of medieval swords. Now and then there is an unexpected treat, such as Alan Williams' recent article on armor metallurgy.
Man at Arms 54 East School Street; Woonsocket, RI 02895, USA has been publishing more sword articles lately, including one about the Castillon sword group, and also includes occasional museum profiles and news and auction announcements and highlights of auction results. An arms show calender looking forward several months is also included.