Sources

Shell buttons are not usually easy to find. However, Home Sew carries two sizes of mother-of-pearl buttons at reasonable prices.

Fabric that has a period look can be found at some chain sewing stores (particularly floral and plaid designs). However, if you're looking for more heirloom quality fabrics, such as voile and batiste, you may need to do some searching online for companies that carry heirloom fabrics. One company that carries period cottons is Reproduction Fabrics. (Note: Though I have not ordered from this company, its reputation is established.)

Twill tape is not common in its linen or cotton form in most chain fabric stores. I've handled both the polyester (which is readily available) and cotton, and recommend the cotton hands down. It can be molded and performs much better than the polyester. If you can't find it locally, be sure to check online, as many purveyors of reproduction goods for reenactors sell it by the yard in varying widths.

Narrow piping is used extensively on the gowns in Wives and Daughters. It's much finer than most piping that is available in most sewing stores today. Heirloom sewing and smocking shops carry it as 'baby cord'. You might obtain the same effect by using a narrow, natural fiber yarn; I've also heard that a good alternative is crochet thread.

Lace is also used extensively in these costumes. For some of the more intricate laces, such as the lace collar on Molly's white evening gown, you can keep your eyes open for similar laces at antique shops, flea markets, and even online dealers. Another option is to piece lace motifs together to make one large collar.