Where to see railway and travel posters:
The National Railway Museum, York
Vintage British Railway Posters at Georgetown University

Where to see railway and steam collections:
London's Transport Museum
UK Heritage Railways

Auction Houses hosting specialist travel and poster sales:
Christies
Bloomsbury Book Auctions
Sheffield Railwayana Auctions
Onslows

Academic expertise and research:
Institute of Railway Studies & Transport History
Institute for Transport Studies
Advanced Railway Research Centre
Association pour l'histoire des chemins de fer en France