Glassine is available at a couple of UK-based bookbinders such as
Ratchford - http://www.ratchford.co.uk/subcategoryd ... spx?id=137
Shepherds Falkiners - http://store.falkiners.com/store/produc ... ain-40gsm/ and Archival Glassine - http://store.falkiners.com/store/produc ... ine-40gsm/