Armortek

There's not many I can add to Stephen's extensive list, but here's a few:

Modelling Supplies
S3i (UK) - https://www.s3i.co.uk/index (stainless steel shackles)
Simply Bearings (UK) - https://simplybearings.co.uk/shop/shopping_cart.php

Suppliers - 1/6th Scale Figures and Equipment
Field of Armor (US) - http://www.fieldofarmortanks.com/
Flags and Patches 172 (eBay) - http://www.ebay.co.uk/usr/flagsandpatches172 (cap badges, unit insignia)
Banjoman (eBay) - http://www.ebay.co.uk/usr/banjoman1000 (headgear)
Tony Barton - http://www.antheads.co.uk/ (cap badges and uniforms)
Churchill Creations - http://www.churchillcreations.co.uk/animatronics.html (Animatronics)

Archives / Research Sites
Achtung Panzer ! - http://www.achtungpanzer.com/achtung-panzer-home
Landships: British Tank Actions of WW1 - https://sites.google.com/site/landships/home
The Tank of Flesquieres (D51 Deborah) - http://www.tank-cambrai.com/english/home.php
Commonwealth War Graves Commission - https://www.cwgc.org/
Imperial War Museum: Collections online - https://www.iwm.org.uk/collections
Liddle Hart Military Archives - http://www.kingscollections.org/catalogues/lhcma
International Committee of the Red Cross: Prisoners of WW1 - https://grandeguerre.icrc.org/
The Gazette (Military Awards) - https://www.thegazette.co.uk/

All the best,

Chris