Jessamyn’s Regency Costume Companion: A must read.
The Regency Fashion Page: Another must read.
Demode Couture: A huge list of extant costumes, sorted by date.
Katherine’s Dress Site: A wonderful collection of Katherine’s reproductions as well as notes on how she created them.
La Couturière Parisienne: A wonderful research site with costumes from every era.
Jane Austen Center Magazine: Great for articles on everyday life with a few costume pieces.
They’re are many more sites out there, but these should get you started.
BR Exports: Silks galore.
Joann’s Fabrics in Portland Oregon: A good resource for muslin. They also have 100% silks in their Home Dec department. You can get a great deal if you catch them having a 50% off sale.
Mill End: Pretty much everything you can imagine.
Fabric Dept: Beautiful voiles that work very well for Regency. They also have an outdoor sale during the summer where you can find some wonderful deals.
Reproduction Fabrics: A great resource for historical reproduction fabrics.
There are good movies and bad movies out there, so be careful if you decide to make a movie costume. Here are some resources for reviews.
The Period Movie Review: Great for costumes and research.
The Costumer’s Guide to Movie Costumes: A wonderful feast for the eyes. Make sure you do your research before deciding to reproduce a movie gown.