Fashion Design Collections in the Kellen Design Archives of the New School (NYC).                                                        Great collection featuring the illustrations of designers from the mid-to late 20th century (American) https://guides.library.newschool.edu/c.php?g=274421&p=1830618

Fashion Illustrations and Drawings from the Victoria and Albert Museum (London, UK)

http://collections.vam.ac.uk/search/?category%5B0%5D=THES48957&material%5B0%5D=x30618&narrow=1&offset=0