I love to study photos of original garments to get inspiration. Some of my favourite resources are - 

Extant Garments

The Metropolitan Museum of Art

Old Sturbridge Village
Colonial Williamsburg®
V&A Search the Collections

Augusta Auctions

National Trust Collections - this search includes the Wade and Snowhill Collection as seen in Janet Arnold Books

All The Pretty Dresses - an awesome blog that posts multiple and detailed pictures of extant gowns

Online Draft-able Patterns

Original Pre 1929 Historical Pattern Collection - great resource for drafting late Victorian and Edwardian Dresses
Commercial Pattern Archive - A collection of scans of pattern covers dating back to 1860, excellent for drafting