"First Class: The Meeting", 1855, by Abraham Solomon |
The best starting reference I've found is Mrs. Kessinger's wardrobe guide. Several of the on-line discussion spaces named in the ladies' posts also address gents' attire, ie, The Sewing Academy, The Civilian Civil War Closet (you do need to log onto Facebook to view the latter). As always, researching a subject before buying anything is advised.
For purchasing garments, NJ Sekela and Jas. Townshend appear to be the premiere outfitters, though I cannot speak from personal experience (note that Townshend covers a wide range of years, and not all items are suitable for ACW use, or for all impressions therein). Kay Gnagey also has some gentlemen's ready-made items.
To those looking to make their own clothing, Jim Ruley's picture-heavy Tailoring Tutorials can help the novice tailor. Rumor has it that the gentleman himself also drafts custom patterns for hire. Past Patterns has several men's patterns available for the 1850s-1860s, and I've heard good things about their vest pattern #018. Peachtree Merchantile patterns are based on original garments, including trousers and an overcoat. Martha McCain's "Fashion Historian" patterns for Simplicity, though now out of print, included several men's patterns with good shapes. Thoughts on Men's Shirts in America, 1750-1900 by Brown and Chamberlain is apparently the definitive work on the subject, though sadly out of print.
Original patterns/tailoring systems online include Devere's The Tailor's Guide (1855) and these from the 1840s. Most plain-sewing books include instructions for men's shirts, though their usefulness varies: The Workwoman's Guide (1840) is the most extensive; The Sampler (1855) actually includes cutting diagrams, though Plain Needle-Work (1852) has a nice finished illustration.