Please note that some of these vendors only carry one or two items which are useful to rapier fighters. When in doubt, always check with your local marshal.
ARMOR:
Castle Garden Creations
Gipsy Peddler
Linen Armor Mercantile Company
Revival Enterprises
Zen Warrior Armory
BOOTS:
Boots by Bohemond
Sofi's Stitches
GORGETS/HOODS:
By The Sword (gorget)
The Renaissance Store (hood)
MASKS:
Absolute Fencing Gear
American Fencers Supply
Fencing.net
MISCELLANEOUS ACCESSORIES:
Bandguns.com (rubber band guns)
Hatcrafters.com (hats)
Jas. Townsend & Son, Inc. (wool over-the-knee socks)
Misc. Etc. (rapier armor drop tester)
SWORDS:
Alchem, Inc.
Arms & Armor
By the Sword (note: not all of these swords are legal in the SCA)
Darkwood Armory
James the Just (note: adding rubber band guns as well)
Popinjay's
Sunshadow Designs (note: they also carry rubber band guns)
Tattershall Arms
Zen Warrior Armory
FOR YOUTH RAPIER - TO CONTACT OUR KINGDOM YOUTH RAPIER MARSHAL
FOR YOUTH RAPIER - PLASTIC FOILS:
Zivkovic
Leon Paul USA (More expensive - but it's black, if that's important to you)
Fencing.net (best price)
FOR YOUTH RAPIER - MASKS:
FenceSmart (carries masks in small sizes)
FOR YOUTH RAPIER - GLOVES:
Absolute Fencing Gear